Liquid crystal display device

ABSTRACT

The liquid crystal display device of this invention includes a plurality of picture element regions each defined by a first electrode provided on a face of a first substrate facing a liquid crystal layer and a second electrode provided on a second substrate so as to oppose the first electrode via the liquid crystal layer sandwiched therebetween. In each of the picture element regions, the first electrode has a plurality of openings and a solid portion, the liquid crystal layer is in a vertical orientation state when no voltage is applied between the first electrode and the second electrode, and when a voltage is applied between the first electrode and the second electrode, a plurality of liquid crystal domains each in a radially-inclined orientation state are respectively formed in the plurality of openings and the solid portion by inclined electrode fields generated at respective edge portions of the openings of the first electrode.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a liquid crystal display device,and more particularly, it relates to a liquid crystal display devicehaving a wide viewing angle characteristic capable of producing a highquality display.

[0002] Recently, a thin and light liquid crystal display device is usedas a display device for a display of a personal computer and a displayunit of portable information terminal equipment. Conventional twistnematic (TN) or super twist nematic (STN) liquid crystal display deviceshave, however, a disadvantage of a narrow viewing angle, and varioustechniques have been developed for overcoming this disadvantage.

[0003] A typical technique to improve the viewing angle characteristicof a TN or STN liquid crystal display device is a method of additionallyproviding an optical compensator. Another technique is a lateral fieldmethod of applying, through a liquid crystal layer, an electric field ina direction horizontal to the substrate surface. Liquid crystal displaydevices of the lateral field method are recently mass-produced andregarded as promising devices. A still another technique is DAP(deformation of vertical aligned phase) in which a nematic liquidcrystal material with negative dielectric anisotropy is used as a liquidcrystal material and a vertical alignment film is used as an alignmentfilm. The DAP is a kind of an ECB (electrically controlledbirefringence) method, and the transmittance is controlled by utilizingthe birefringent property of the liquid crystal molecules.

[0004] Although the lateral field method is one of effective methods forincreasing the viewing angle, the production margin is very small in theproduction process as compared with that of a general TN liquid crystaldisplay device, and hence, there is a difficulty in stable production ofthis type of liquid crystal display devices. This is because gapirregularity between substrates and shift of the transmission axis of apolarizing plate (polarization axis) from the orientation axis of aliquid crystal molecule largely affect the luminance and the contrastratio of display. In order to stably produce the liquid crystal displaydevices of the lateral field method by highly precisely controllingthese factors, the technique should be further highly developed.

[0005] In order to produce an even display free from display unevennessby a liquid crystal display device of the DAP method, it is necessary tocontrol orientation. For controlling the orientation, an alignmenttreatment is carried out by rubbing the surface of an alignment film.When the surface of a vertical alignment film is subjected to a rubbingtreatment, however, rubbing streaks are easily caused in a displayedimage. Therefore, this treatment is not suitable to mass-production.

[0006] On the other hand, for controlling the orientation without therubbing treatment, a method for controlling the orientation direction ofliquid crystal molecules by an inclined electric field generated byforming a slit (opening) in an electrode has been proposed (as describedin, for example, Japanese Laid-Open Patent Publication Nos. 6-301036 and2000-47217). However, the present inventors have found the following asa result of examination: The orientation state of a region of a liquidcrystal layer corresponding to the opening of the electrode is notspecified in the methods disclosed in these publications, and thecontinuity of the orientation of the liquid crystal molecules is notsufficient. Therefore, it is difficult to obtain a stable orientationstate over an entire picture element, and hence, a displayed imagebecomes disadvantageously uneven.

SUMMARY OF THE INVENTION

[0007] The present invention was devised to overcome the aforementioneddisadvantages, and an object of the invention is providing a liquidcrystal display device having a wide viewing angle characteristic andhigh display quality.

[0008] The liquid crystal display device of this invention includes afirst substrate; a second substrate; a liquid crystal layer disposedbetween the first substrate and the second substrate; and a plurality ofpicture element regions each defined by a first electrode provided on aface of the first substrate facing the liquid crystal layer and a secondelectrode provided on the second substrate so as to oppose the firstelectrode via the liquid crystal layer sandwiched therebetween, and thefirst electrode includes a plurality of openings and a solid portion ineach of the plurality of picture element regions, the liquid crystallayer is in a vertical orientation state in each of the plurality ofpicture element regions when no voltage is applied between the firstelectrode and the second electrode, and when a voltage is appliedbetween the first electrode and the second electrode, a plurality ofliquid crystal domains each in a radially-inclined orientation state areformed in the plurality of openings and the solid portion by inclinedelectric fields generated at respective edge portions of the pluralityof openings of the first electrode, for producing a display by changingorientation states of the plurality of liquid crystal domains inaccordance with the applied voltage. Owing to this structure, theaforementioned object is achieved.

[0009] Preferably, at least some of the plurality of openings havesubstantially the same shape and the same size, and form at least oneunit lattice arranged so as to have rotational symmetry.

[0010] Preferably, each of the at least some of the plurality ofopenings is in a rotationally symmetrical shape.

[0011] Each of the at least some of the plurality of openings may be ina substantially circular shape.

[0012] Each region of the solid portion surrounded with the at leastsome of the plurality of openings (a unit solid portion) may be in asubstantially circular shape.

[0013] Each region of the solid portion surrounded with the at leastsome of the plurality of openings (a unit solid portion) may be in asubstantially rectangular shape with substantially arc-shaped corners.

[0014] Preferably, in each of the plurality of picture element regions,a total area of the plurality of openings of the first electrode issmaller than an area of the solid portion of the first electrode.

[0015] The liquid crystal display device may further include aprotrusion within each of the plurality of openings, a cross-sectionalshape of the protrusion taken along a plane direction of the substratemay be the same as a shape of the corresponding opening, and a side faceof the protrusion may have an orientation-regulating force for orientingliquid crystal molecules of the liquid crystal layer in the samedirection as an orientation-regulating direction obtained by theinclined electric field.

[0016] Preferably, the plurality of liquid crystal domains are in aspirally radially-inclined orientation state.

[0017] The liquid crystal display device may further include a pair ofpolarizing plates respectively provided outside of the first substrateand the second substrate and disposed with polarizing axes thereofcrossing each other substantially perpendicularly, and in each of theplurality of liquid crystal domains, assuming that a liquid crystalmolecule included in the liquid crystal layer and positioned in a 12o'clock direction on a display surface in regard to a center of each ofsaid plurality of liquid crystal domains is inclined against the 12o'clock direction on the display surface by an angle θ, the polarizationaxis of one of the pair of polarizing plates is preferably inclined inthe same direction as inclination of the liquid crystal moleculepositioned in the 12 o'clock direction on the display surface by anangle exceeding 0 degree and smaller than 2θ against the 12 o'clockdirection on the display surface.

[0018] More preferably, the polarization axis of one of the pair ofpolarizing plates is inclined by an angle exceeding 0 degree and equalto θ or less. Alternatively, the polarization axis of one of the pair ofpolarizing plates may be inclined by an angle substantially the same asθ/2 or the polarization axis of one of the pair of polarizing plates maybe inclined by an angle substantially the same as θ.

[0019] The solid portion may include a plurality of island portionsarranged in the form of an m×n matrix and a plurality of branch portionsfor electrically connecting adjacent pairs of the plurality of islandportions, and the number of the plurality of branch portions may besmaller than (2mn−m−n).

[0020] The first substrate can further include an active elementprovided correspondingly to each of the plurality of picture elementregions, and the first electrode may correspond to a picture elementelectrode provided in each of the plurality of picture element regionsto be switched by the active element and the second electrode maycorrespond to at least one counter electrode opposing the plurality ofpicture element electrodes.

[0021] The other liquid crystal display device of this inventionincludes a first substrate; a second substrate; a liquid crystal layerdisposed between the first substrate and the second substrate; and aplurality of picture element regions each defined by a first electrodeprovided on a face of the first substrate facing the liquid crystallayer and a second electrode provided on the second substrate so as tooppose the first electrode via the liquid crystal layer sandwichedtherebetween, and in each of the plurality of picture element regions,the liquid crystal layer is in a vertical orientation state when novoltage is applied between the first electrode and the second electrode,and the first electrode includes a plurality of openings disposed atleast corners of each of the plurality of picture element regions and asolid portion. Owing to this structure, the aforementioned object isachieved.

[0022] Preferably, a region of the solid portion surrounded with atleast some of the plurality of openings is in a rotationally symmetricalshape.

[0023] Alternatively, a region of the solid portion surrounded with atleast some of the plurality of openings may be in a substantiallycircular shape.

[0024] Alternatively, a region of the solid portion surrounded with atleast some of the plurality of openings may be in a substantiallyrectangular shape with substantially arc-shaped corners.

[0025] The solid portion may include a plurality of island portionsarranged in the form of an m×n matrix and a plurality of branch portionsfor electrically connecting adjacent pairs of the plurality of islandportions, and the number of the plurality of branch portions may besmaller than (2mn−m−n).

[0026] The functions of the present invention are as follows:

[0027] In the present liquid crystal display device, one of a pair ofelectrodes for applying a voltage through a liquid crystal layer in apicture element region includes a plurality of openings (where noconducting film is present in the electrode) and a solid portion (aportion other than the openings where a conducting film is present inthe electrode). The solid portion is typically formed from a continuousconducting film. The liquid crystal layer is in a vertical orientationstate when no voltage is applied, and when a voltage is applied, aplurality of liquid crystal domains each in a radially-inclinedorientation state are formed by inclined electric fields generated atthe respective edge portions of the openings of the electrode.Typically, the liquid crystal layer is formed from a liquid crystalmaterial having negative dielectric anisotropy and is controlled in itsorientation by vertical alignment films sandwiching the liquid crystallayer.

[0028] The liquid crystal domains formed by the inclined electric fieldsare formed in regions corresponding to the openings and the solidportion of the electrode, and a display is produced by changing theorientation states of these liquid crystal domains in accordance withthe applied voltage. Since each of the liquid crystal domains isoriented axially symmetrically, the viewing angle dependency of displayquality can be reduced so as to attain a wide viewing anglecharacteristic.

[0029] Furthermore, since the liquid crystal domains formedcorrespondingly to the openings and the liquid crystal domains formedcorrespondingly to the solid portion are formed owing to the inclinedelectric fields generated at the respective edge portions of theopenings, these liquid crystal domains are formed adjacently andalternately and the orientations of liquid crystal molecules of theadjacent liquid crystal domains are substantially continuous.Accordingly, no disclination line is formed between a liquid crystaldomain formed correspondingly to an opening and a liquid crystal domainformed correspondingly to a solid portion. Therefore, degradation in thedisplay quality due to a disclination line can be avoided, and theorientation of the liquid crystal molecules is highly stable.

[0030] In the present liquid crystal display device, the liquid crystalmolecules are placed in the radially-inclined orientation state not onlyin a region corresponding to the solid portion of the electrode but alsoin regions corresponding to the openings. Therefore, as compared withthe aforementioned conventional liquid crystal display device, thecontinuity in the orientations of the liquid crystal molecules is higherand the orientation state is more stable, so as to realize even displayfree from unevenness. In particular, it is necessary to allow theinclined electric field for controlling the orientation of the liquidcrystal molecules to work on a large number of liquid crystal moleculesin order to realize a good response characteristic (namely, a highresponse speed), and for this purpose, it is necessary to form a largenumber of openings (edge portions). In the present liquid crystaldisplay device, liquid crystal domains that can be placed in a stableradially-inclined orientation state can be formed correspondingly to theopenings, and hence, even when a large number of openings are formed forimproving the response characteristic, the degradation of displayquality (occurrence of unevenness) can be avoided.

[0031] When at least some of the plural openings have substantially thesame shape and the same size so as to form at least one unit latticerotationally symmetrically arranged, the plurality of liquid crystaldomains can be highly symmetrically arranged by using the unit latticeas a unit, resulting in improving the viewing angle dependency of thedisplay quality. Furthermore, when the entire picture element region isdivided into unit lattices, the orientation of the liquid crystal layercan be stabilized over the entire picture element region. For example,the openings are arranged so that the centers of the respective openingscan form a square lattice. In the case where one picture element regionis divided by opaque composing elements such as a storage capacitanceline, a unit lattice is disposed in each region that makes contributionto the display.

[0032] When each of at least some of the plurality of openings(typically, the openings together forming a unit lattice) is in arotationally symmetrical shape, the stability of the radially-inclinedorientation of the liquid crystal domain formed correspondingly to theopening can be improved. For example, the shape (seen from the substratenormal direction) of each opening is a circle or a regular polygon (suchas a square). The opening may be in a shape not rotationally symmetrical(such as an ellipse) depending upon the shape (the ratio between widthand length) of a picture element. Furthermore, when a region of thesolid portion substantially surrounded with the openings (“a unit solidportion” described below) is in a rotationally symmetrical shape, thestability of the radially-inclined orientation of the liquid crystaldomain formed correspondingly to the solid portion can be improved. Forexample, in the case where the openings are disposed in a square latticearrangement, the opening may be in a substantially star-shape orcross-shape and the solid portion may be in a substantially circular orsquare shape. Needless to say, both the opening and the portion of thesolid portion surrounded with the openings may be in a substantiallysquare shape.

[0033] In order to stabilize the radially-inclined orientation of theliquid crystal domain formed correspondingly to the opening of theelectrode, the liquid crystal domain formed correspondingly to theopening is preferably in a substantially circular shape. Converselyspeaking, the shape of the opening is designed so as to form asubstantially circular liquid crystal domain correspondingly to theopening.

[0034] Needless to say, in order to stabilize the radially-inclinedorientation of the liquid crystal domain formed correspondingly to thesolid portion of the electrode, the region of the solid portionsubstantially surrounded with the openings is preferably in asubstantially circular shape. One liquid crystal domain formed in thesolid portion made from a continuous conducting film is formedcorrespondingly to the region of the solid portion substantiallysurrounded with the plural openings (unit solid portion). Accordingly,the shapes and the arrangement of the openings are determined so thatthe region of the solid portion (unit solid portion) can be in asubstantially circular shape.

[0035] In any of the aforementioned cases, the sum of the areas of theopenings formed in the electrode is preferably smaller than the area ofthe solid portion in each of the picture element regions. As the area ofthe solid portion is larger, the area of the liquid crystal layer(defined on a plane seen from the substrate normal direction) directlyaffected by the electric fields generated by the electrodes is larger,and hence, the optical characteristic (such as transmittance) of theliquid crystal layer against voltage can be improved.

[0036] It is preferably determined whether the opening is formed in asubstantially circular shape or the unit solid portion is formed in asubstantially circular shape depending upon the area of the solidportion is larger in which structure. It is appropriately selected whichstructure is preferred depending upon the pitch of picture elements.Typically, in the case where the pitch exceeds approximately 25 μm, theopenings are preferably formed so as to form substantially circular unitsolid portions, and in the case where the pitch is smaller thanapproximately 25 μm, the openings are preferably formed in substantiallycircular shape.

[0037] When the region of the solid portion substantially surroundedwith the openings is formed in a substantially rectangular shape withsubstantially arc-shaped corners, the radially-inclined orientation canbe stabilized and the transmittance (effective aperture ratio) can beimproved.

[0038] The orientation-regulating force caused by the inclined electricfield generated at the edge portion of the opening of the electrodeworks merely under voltage application. Therefore, when, for example, anexternal force is applied to the liquid crystal panel under applicationof no voltage or a comparatively low voltage, the radially-inclinedorientation of the liquid crystal domain sometimes may not be kept. Inorder to overcome this problem, in one preferred embodiment, the liquidcrystal display device includes a protrusion formed within the openingof the electrode and having orientation-regulating force on the liquidcrystal molecules of the liquid crystal layer in the same direction asthe orientation-regulating direction of the inclined electric field. Thecross-sectional shape of the protrusion taken on a plane direction ofthe substrate is the same as the opening, and is preferably in arotationally symmetrical shape similarly to the shape of the opening.

[0039] When the plurality of liquid crystal domains can be placed in aspiral radially-inclined orientation state, the orientation can befurther stabilized, further even display free from unevenness can berealized and the response speed is increased. The spiralradially-inclined orientation state can be realized by using a nematicliquid crystal material having negative dielectric anisotropy includinga chiral agent. It depends upon the kind of chiral agent whether thespiral direction is the clockwise direction or the counterclockwisedirection.

[0040] In the case where the liquid crystal display device having theaforementioned structure further includes a pair of polarizing platesprovided on the outside of the first and second substrates to have theirpolarization axes crossing substantially perpendicularly, the displayquality can be further improved as follows:

[0041] Specifically, when a liquid crystal molecule positioned in the 12o'clock direction on the display surface in regard to the center of theliquid crystal domain is assumed to be inclined against the 12 o'clockdirection on the display surface by an angle θ, the polarizing platesare arranged so that the polarization axis of one of the polarizingplates is inclined in the same direction as the incline direction of theliquid crystal molecule against the 12 o'clock direction on the displaysurface by an angle exceeding 0 degree and smaller than 2θ. Thus, thelight transmittance obtained when the liquid crystal domain is in thespiral radially-inclined orientation state can be improved, resulting inrealizing bright display. In particular, when the polarizing plates arearranged so that the polarization axis of one polarizing plate isinclined at an angle substantially the same as θ, the lighttransmittance can be further increased, resulting in further brightdisplay. Furthermore, when the polarizing plates are arranged so thatthe polarization axis of one polarizing plate is inclined by an angleexceeding 0 degree and equal to θ or less, not only bright display canbe realized but also occurrence of a tailing phenomenon (including awhite tailing phenomenon and a black tailing phenomenon) can besuppressed, resulting in realizing display with high quality. Inparticular, when the polarizing plates are arranged so that thepolarization axis of one polarizing plate is inclined at an anglesubstantially the same as θ/2, the occurrence of the white tailingphenomenon and the black tailing phenomenon can be substantiallyavoided, resulting in realizing display with further higher quality.

[0042] The solid portion of the electrode is composed of, for example, aplurality of island portions and a plurality of branch portions each forelectrically connecting an adjacent pair of the plurality of islandportions. Since each branch portion present between the adjacent islandportions degrades the orientation-regulating effect attained by theinclined electric field, the degradation of the orientation-regulatingeffect can be suppressed so as to improve the response characteristic asthe width of each branch portion is smaller and the number of branchportions is smaller.

[0043] In the case where the plurality of island portions are arrangedin the form of an m×n matrix, if the branch portions are providedbetween all the adjacent pairs of island portions, the number of branchportions is (2mn−m−n). When the number of plurality of branch portionsis smaller than (2mn−m−n), the degradation of the orientation-regulatingeffect can be suppressed so as to improve the response characteristic.

[0044] The liquid crystal display device of this invention is, forexample, an active matrix liquid crystal display device equipped with aswitching element such as a TFT in each picture element region, and theelectrode having the openings corresponds to a picture element electrodeconnected to the switching element and the other electrode correspondsto at least one counter electrode opposing a plurality of pictureelement electrodes. In this manner, merely by forming openings in one ofthe pair of electrodes opposing each other via the liquid crystal layersandwiched therebetween, stable radially-inclined orientation can berealized. Specifically, the present liquid crystal display device can befabricated by a known fabrication method merely by modifying a photomaskused in patterning a conducting film into a pattern of picture elementelectrodes so as to form openings in a desired shape in desiredarrangement. Needless to say, a plurality of openings may be formed inthe counter electrode.

[0045] In the other liquid crystal display device of this invention, oneof the pair of electrodes for applying a voltage through the liquidcrystal layer in a picture element region includes a plurality ofopenings disposed at least at corners of the picture element region anda solid portion. Therefore, when a voltage is applied between the pairof electrodes, inclined electric fields are generated at the edgeportions of the openings of the electrode. Accordingly, owing to theinclined electric fields generated at the edge portions of the pluralityof openings disposed at least at the corners, the liquid crystal layeris formed into liquid crystal domains each in a radially-inclinedorientation state under voltage application, resulting in attaining awide viewing angle characteristic.

[0046] A unit solid portion (a region of the solid portion substantiallysurrounded with the openings) present in a given picture element regionmay be a plurality of unit solid portions or a single unit solid portionsurrounded with the openings disposed at the corners. In the case wherea unit solid portion present in a given picture element region is asingle unit solid portion, the openings surrounding the unit solidportion may be a plurality of openings disposed at the corners or asubstantially single opening continuously formed from a plurality ofopenings disposed at the corners.

[0047] When the region of the solid portion substantially surroundedwith the openings (unit solid portion) is in a rotationally symmetricalshape, the stability of the radially-inclined orientation of the liquidcrystal domain formed in the solid portion can be improved. For example,the unit solid portion may be in a substantially circular shape, asubstantially square shape or a substantially rectangular shape.

[0048] When the unit solid portion is in a substantially circular shape,the radially-inclined orientation of the liquid crystal domain formed inthe solid portion of the electrode can be stabilized. Since a liquidcrystal domain formed in the solid portion made from a continuousconducting film is formed correspondingly to the unit solid portion, theshape and the arrangement of the openings are determined so that theunit solid portion can be formed in a substantially circular shape.

[0049] Furthermore, when the unit solid portion is in a substantiallyrectangular shape with substantially arc-shaped corners, theradially-inclined orientation can be stabilized and the transmittance(effective aperture ratio) can be improved.

[0050] The solid portion of the electrode is composed of, for example, aplurality of island portions and a plurality of branch portions each forelectrically connecting an adjacent pair of the plurality of islandportions. Since each branch portion present between the adjacent islandportions degrades the orientation-regulating effect attained by theinclined electric field, the degradation of the orientation-regulatingeffect can be suppressed so as to improve the response characteristic asthe width of each branch portion is smaller and the number of branchportions is smaller.

[0051] In the case where the plurality of island portions are arrangedin the form of an m×n matrix, if the branch portions are providedbetween all the adjacent pairs of island portions, the number of branchportions is (2mn−m−n). When the number of plurality of branch portionsis smaller than (2mn−m−n), the degradation of the orientation-regulatingeffect can be suppressed so as to improve the response characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0052]FIG. 1A is a top view for schematically showing the structure ofone picture element region of a liquid crystal display device 100according to Embodiment 1 of the invention, and FIG. 1B is across-sectional view thereof taken along line 1B-1B′ of FIG. 1A;

[0053]FIGS. 2A and 2B are diagrams for showing states where a voltage isapplied through a liquid crystal layer 30 of the liquid crystal displaydevice 100, and specifically FIG. 2A schematically shows a state whereorientation starts to change (ON initial state) and FIG. 2Bschematically shows a stationary state;

[0054]FIGS. 3A, 3B, 3C and 3D are diagrams for schematically showing therelationship between a line of electric force and orientation of liquidcrystal molecules;

[0055]FIGS. 4A, 4B and 4C are diagrams for schematically showingorientation states of liquid crystal molecules seen from a substratenormal direction in the liquid crystal display device 100 of Embodiment1;

[0056]FIGS. 5A, 5B and 5C are diagrams for schematically showingexamples of radially-inclined orientation of liquid crystal molecules;

[0057]FIGS. 6A and 6B are top views for schematically showing otherpicture element electrodes usable in the liquid crystal display deviceof Embodiment 1;

[0058]FIGS. 7A and 7B are top views for schematically showing stillother picture element electrodes usable in the liquid crystal displaydevice of Embodiment 1;

[0059]FIGS. 8A and 8B are top views for schematically showing stillother picture element electrodes usable in the liquid crystal displaydevice of Embodiment 1;

[0060]FIG. 9 is a top view for schematically showing still anotherpicture element electrode usable in the liquid crystal display device ofEmbodiment 1;

[0061]FIGS. 10A and 10B are top views for schematically showing stillother picture element electrodes usable in the liquid crystal displaydevice of Embodiment 1;

[0062]FIG. 11A is a diagram for schematically showing a unit lattice ofa pattern shown in FIG. 1A, FIG. 1B is a diagram for schematicallyshowing a unit lattice of a pattern shown in FIG. 9, and FIG. 11C is agraph for showing the relationship between a pitch p and an area ratioof a solid portion;

[0063]FIG. 12A is a diagram for schematically showing a unit lattice ofa picture element electrode having a unit solid portion formed in asubstantially circular shape, FIGS. 12B and 12C are diagrams forschematically showing unit lattices of picture element electrodes havingunit solid portions formed in a substantially square shape withsubstantially arc-shaped corners, and FIG. 12D is a diagram forschematically showing a unit lattice of a picture element electrodehaving a unit solid portion formed in a substantially square shape;

[0064]FIG. 13A is a top view for schematically showing the structure ofone picture element region of a liquid crystal display device 200according to Embodiment 2 of the invention, and FIG. 13B is across-sectional view thereof taken along line 13B-13B′ of FIG. 13A;

[0065]FIGS. 14A, 14B, 14C and 14D are schematic diagrams for explainingthe relationship between orientation of a liquid crystal molecule 30 aand the shape of a surface with a vertical alignment property;

[0066]FIGS. 15A and 15B are diagrams for showing states where a voltageis applied through a liquid crystal layer 30 of the liquid crystaldisplay device 200, and specifically FIG. 15A schematically shows astate where orientation starts to change (ON initial state) and FIG. 15Bschematically shows a stationary state;

[0067]FIGS. 16A, 16B and 16C are respectively schematic cross-sectionalviews of liquid crystal display devices 200A, 200B and 200C ofEmbodiment 2 that are different in the arrangement of an opening and aprotrusion;

[0068]FIG. 17 is a cross-sectional view for schematically showing thecross-sectional structure of the liquid crystal display device 200 takenalong line 17A-17A′ of FIG. 13A;

[0069]FIGS. 18A and 18B are diagrams for schematically showing thestructure of one picture element region of a liquid crystal displaydevice 200D according to Embodiment 2, and specifically FIG. 18A is atop view thereof and FIG. 18B is a cross-sectional view thereof takenalong line 18B-18B′ of FIG. 18A;

[0070]FIG. 19A is a diagram for schematically showing an orientationstate of liquid crystal molecules obtained immediately after voltageapplication, and FIGS. 19B and 19C are top views for schematicallyshowing orientation sates of liquid crystal molecules in orientationstable time (stationary state);

[0071]FIG. 20 is a graph in which the ordinate indicates thetransmittance in a white display state of a liquid crystal displaydevice according to an embodiment of the invention and the abscissaindicates the angle of a polarization axis against the 12 o'clockdirection;

[0072]FIG. 21A is a diagram for schematically showing arrangement of apolarizing plate and FIG. 21B is a diagram for schematically showingshade regions SR in a liquid crystal domain obtained when the polarizingplate is arranged as shown in FIG. 21A;

[0073]FIG. 22A is a diagram for schematically showing anotherarrangement of a polarizing plate and FIG. 22B is a diagram forschematically showing shade regions SR in a liquid crystal domainobtained when the polarizing plate is arranged as shown in FIG. 22A;

[0074]FIG. 23 is a diagram for schematically showing a white tailingphenomenon;

[0075]FIG. 24 is a diagram for schematically showing the state where thetailing phenomenon is prevented in a liquid crystal display device ofthe invention;

[0076]FIG. 25A is a diagram for schematically showing arrangement of apolarizing plate, FIG. 25B is a diagram for schematically showing shaderegions SR obtained immediately after voltage application when thepolarizing plate is arranged as shown in FIG. 25A, and FIG. 25C is adiagram for schematically showing shade regions. SR obtained in theorientation stable time (stationary state) when the polarizing plate isarranged as shown in FIG. 25A;

[0077]FIG. 26A is a diagram for schematically showing arrangement of apolarizing plate, FIG. 26B is a diagram for schematically showing shaderegions SR obtained immediately after voltage application when thepolarizing plate is arranged as shown in FIG. 26A, and FIG. 26C is adiagram for schematically showing shade regions SR obtained in theorientation stable time (stationary state) when the polarizing plate isarranged as shown in FIG. 26A;

[0078]FIG. 27 is a graph for showing change with time of thetransmittance in accordance with change of a picture element region froma black display state to a intermediate gray scale display stateobtained when the angle of the polarization axis against the 12 o'clockdirection is 0 degree, approximately 13 degrees or approximately 20degrees;

[0079]FIG. 28 is a diagram for schematically showing a black tailingphenomenon;

[0080]FIG. 29 is a top view for schematically showing a picture elementelectrode used in a liquid crystal display device according to anembodiment of the invention;

[0081]FIG. 30 is a top view for schematically showing an orientationstate of liquid crystal molecules under voltage application;

[0082]FIG. 31 is a cross-sectional view taken along line 31A-31A′ or31B-31B′ of FIG. 30 for schematically showing the orientation state ofthe liquid crystal molecules under voltage application;

[0083]FIG. 32 is a top view for schematically showing an orientationstate of liquid crystal molecules under voltage application;

[0084]FIG. 33 is a cross-sectional view taken along line 33A-33A′ or33B-33B′ of FIG. 32 for schematically showing the orientation state ofthe liquid crystal molecules under voltage application;

[0085]FIG. 34 is a top view for schematically showing an orientationstate of liquid crystal molecules under voltage application;

[0086]FIGS. 35A and 35B are cross-sectional views respectively takenalong lines 35A-35A′ and 35B-35B′ of FIG. 34 for schematically showingthe orientation state of the liquid crystal molecules under voltageapplication;

[0087]FIG. 36 is a top view for schematically showing an orientationstate of liquid crystal molecules under voltage application;

[0088]FIG. 37A and 37B are cross-sectional views respectively takenalong lines 35A-35A′ and 35B-35B′ of FIG. 34 for schematically showingthe orientation state of the liquid crystal molecules under voltageapplication;

[0089]FIG. 38 is a top view for schematically showing an orientationstate of liquid crystal molecules under voltage application;

[0090]FIGS. 39A and 39B are top views for schematically showingorientation states of liquid crystal molecules under voltage applicationrespectively obtained when a branch portion of a picture elementelectrode has a comparatively small width and when the branch portion ofthe picture element electrode has a comparatively large width;

[0091]FIG. 40 is a graph for schematically showing change with time oftransmittance under application of voltage through a liquid crystallayer obtained when the branch portion has a comparatively small widthand when the branch portion has a comparatively large width;

[0092]FIGS. 41A and 41B are top views for schematically showing liquidcrystal molecules oriented in a direction parallel to a polarizationaxis in a second stable state respectively obtained when a branchportion 14 d has a comparatively small width and when the branch portion14 d has a comparatively large width;

[0093]FIG. 42 is a top view for schematically showing a picture elementelectrode usable in a liquid crystal display device according to anembodiment of the invention;

[0094]FIG. 43 is a top view for schematically showing another pictureelement electrode usable in the liquid crystal display device accordingto the embodiment of the invention;

[0095]FIG. 44 is a top view for schematically showing still anotherpicture element electrode usable in the liquid crystal display deviceaccording to the embodiment of the invention;

[0096]FIG. 45 is a top view for schematically showing still anotherpicture element electrode usable in the liquid crystal display deviceaccording to the embodiment of the invention; and

[0097]FIG. 46 is a top view for schematically showing still anotherpicture element electrode usable in the liquid crystal display deviceaccording to the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0098] Preferred embodiments of the invention will now be described withreference to the accompanying drawings.

Embodiment 1

[0099] First, the electrode structure of a liquid crystal display deviceof this invention and the function thereof will be described. The liquidcrystal display device of this invention is suitably used in an activematrix liquid crystal display device owing to its excellent displaycharacteristic. Active matrix liquid crystal display devices using thinfilm transistors (TFTS) will be exemplified in the following preferredembodiments, which does not limit the invention. The invention is alsoapplicable to an active matrix liquid crystal display device using MIMsand a passive matrix liquid crystal display device. Also, in thefollowing embodiments, transmission type liquid crystal display devicesare exemplified, which does not limit the invention. The invention isalso applicable to a reflection type liquid crystal display device and atransmission/reflection type liquid crystal display device describedlater.

[0100] Herein, a region of a liquid crystal display device correspondingto a “picture element”, that is, a minimum unit of display, isdesignated as a “picture element region”. In a color liquid crystaldisplay device, three picture elements of R, G and B together correspondto one pixel. In an active matrix liquid crystal display device, onepicture element region is defined by a picture element electrode and acounter electrode opposing the picture element electrode. Alternatively,in a passive matrix liquid crystal display device, each intersectionregion between column electrodes in a stripe shape and row electrodesprovided perpendicularly to the column electrodes is defined as apicture element region. In a structure employing a black matrix,strictly speaking, a region corresponding to an opening of the blackmatrix in the entire region to which a voltage is applied in accordancewith a state to be displayed corresponds to a picture element region.

[0101] Now, the structure of one picture element region of a liquidcrystal display device 100 according to Embodiment 1 of the inventionwill be described with reference to FIGS. 1A and 1B. In the followingdescription, a color filter and a black matrix are omitted forsimplification. Also, in the drawings referred to in the followingembodiments, like reference numerals are used to refer to like elementshaving substantially the same functions as those of the liquid crystaldisplay device 100, so as to omit the description. FIG. 1A is a top viewseen from the substrate normal direction and FIG. 1B is across-sectional view taken along line 1B-1B′ of FIG. 1A. In FIG. 1B, novoltage is applied through a liquid crystal layer.

[0102] The liquid crystal display device 100 includes an active matrixsubstrate (hereinafter referred to as the TFT substrate) 100 a, acounter substrate (also designated as the color filter substrate) 100 band a liquid crystal layer 30 disposed between the TFT substrate 100 aand the counter substrate 100 b. Liquid crystal molecules 30 a of theliquid crystal layer 30 have negative dielectric anisotropy, and owingto vertical alignment films serving as vertical alignment layers (notshown) provided on the surfaces of the TFT substrate 100 a and thecounter substrate 100 b facing the liquid crystal layer 30, the liquidcrystal molecules 30 a are oriented vertically to the surface of thevertical alignment films as shown in FIG. 1B when no voltage is appliedthrough the liquid crystal layer 30. Such a state of the liquid crystallayer 30 is designated as a vertical orientation state. However,depending upon the kinds of the vertical alignment film and the liquidcrystal material, the liquid crystal molecules 30 a of the liquidcrystal layer 30 in the vertical orientation state may be slightlyinclined against the normal line of the surface of the verticalalignment film (substrate surface). In general, a state where a liquidcrystal molecule is oriented with the liquid crystal molecular axis(also designated as the axial direction) inclined at an angle ofapproximately 85 degrees or more against the surface of a verticalalignment film is designated as the vertical orientation state.

[0103] The TFT substrate 100 a of the liquid crystal display device 100includes a transparent substrate (such as a glass substrate) 11 and apicture element electrode 14 formed thereon. The counter substrate 100 bincludes a transparent substrate (such as a glass substrate) 21 and acounter electrode 22 formed thereon. In accordance with a voltageapplied to each pair of picture element electrode 14 and counterelectrode 22 opposing each other via the liquid crystal layer 30sandwiched therebetween, the orientation state of the liquid crystallayer 30 in each picture element region is changed. A display isproduced by utilizing a phenomenon that the polarizing state and thequantity of light transmitting the liquid crystal layer 30 are changedin accordance with the change of the orientation state of the liquidcrystal layer 30.

[0104] The picture element electrode 14 of the liquid crystal displaydevice 100 has a plurality of openings 14 a and a solid portion 14 b.The opening 14 a corresponds, in the picture element electrode 14 formedfrom a conducting film (such as an ITO film), to a portion where theconducting film is removed, and the solid portion 14 b corresponds to aportion where the conducting film remains (a portion other than theopenings 14 a). A plurality of openings 14 a are formed in each pictureelement electrode, and the solid portion 14 b is basically formed from asingle continuous conducting film.

[0105] The plural openings 14 a are arranged so that their centers forma square lattice, and a region of the solid portion (hereinafterreferred to as the unit solid portion) 14 b′ substantially surroundedwith four openings 14 a whose centers are positioned on four latticepoints forming one unit lattice is in a substantially circular shape.Each opening 14 a is in a substantially star-shape with four quarterarc-shaped edges having a four-fold rotation axis at its center. Theunit lattices are preferably formed up to the edges of the pictureelement electrode 14 in order to stabilize the orientation over theentire picture element region. Accordingly, as shown in the drawing, theedge of the picture element electrode is preferably patterned into ashape corresponding to approximately a half of the opening 14 a (at theside edge of the picture element electrode) or approximately a quarterof the opening 14 a (at the corner edge of the picture elementelectrode).

[0106] The openings 14 a positioned in the center part of the pictureelement region have substantially the same shape and the same size. Theunit solid portions 14 b′ positioned in the unit lattices formed by theopenings 14 a are in a substantially circular shape and havesubstantially the same shape and the same size. The unit solid portions14 b′ adjacent to each other are connected to each other, so as to workas the solid portion 14 b functioning as a substantially singleconducting film.

[0107] When a voltage is applied between the picture element electrode14 having the aforementioned structure and the counter electrode 22, aplurality of liquid crystal domains each having radially-inclinedorientation are formed due to inclined electric fields generated at theedge portions of the openings 14 a. The liquid crystal domains areformed in each region corresponding to each opening 14 a and each regioncorresponding to each unit solid portion 14 b′ within the unit lattice.

[0108] In this embodiment, the picture element electrode 14 in a squareshape is exemplified, but the shape of the picture element electrode 14is not limited to the square. The general shape of the picture elementelectrode 14 is approximate to a rectangle (including a square), andhence, the openings 14 a can be regularly disposed in square latticearrangement. The effect of the invention can be attained even when thepicture element electrode 14 is in a shape other than the rectangularshape as far as the openings 14 a are disposed regularly (for example,in the square lattice arrangement as described above) so as to form theliquid crystal domains over the entire picture element region.

[0109] The mechanism of formation of the liquid crystal domains by theinclined electric fields will now be described with reference to FIGS.2A and 2B. FIGS. 2A and 2B show the states attained by applying avoltage through the liquid crystal layer 30 of FIG. 1B, andspecifically, FIG. 2A schematically shows the state where theorientation of the liquid crystal molecules 30 a starts to change inaccordance with the voltage applied through the liquid crystal layer 30(ON initial state) and FIG. 2B schematically shows the state where theorientation of the liquid crystal molecules 30 a changed in accordancewith the applied voltage attains the stationary state. In FIGS. 2A and2B, a line EQ denotes an equipotential line.

[0110] When the picture element electrode 14 and the counter electrode22 have the same potential (which corresponds to the state where novoltage is applied through the liquid crystal layer 30), the liquidcrystal molecules 30 a within the picture element region are orientedvertically to the surfaces of the substrates 11 and 21 as shown in FIG.1B.

[0111] When a voltage is applied, potential gradient expressed by theequipotential line EQ (perpendicularly crossing a line of electricforce) of FIG. 2A is formed. The equipotential line EQ is parallel tothe surfaces of the solid portion 14 b and the counter electrode 22within a region of the liquid crystal layer 30 positioned between thesolid portion 14 b of the picture element electrode 14 and the counterelectrode 22, and drops in a region corresponding to the opening 14 a ofthe picture element electrode 14. Therefore, the inclined electric fieldexpressed by an inclined portion of the equipotential line EQ is formedin a region of the liquid crystal layer 30 on the edge portion EG of theopening 14 a (that is, the inside periphery of the opening 14 aincluding the boundary thereof).

[0112] To the liquid crystal molecules 30 a having the negativedielectric anisotropy, torque for orienting the axial direction of theliquid crystal molecules 30 a parallel to the equipotential line EQ(vertical to the line of electric force) is applied. Accordingly, theliquid crystal molecules 30 a disposed on the edge portions EG areinclined (rotated) in the clockwise direction at the edge portion EG onthe right hand side in the drawing and in the counterclockwise directionat the edge portion EG on the left hand side in the drawing as shownwith arrows in FIG. 2A, so as to orient parallel to the equipotentialline EQ.

[0113] Now, the change of the orientation of the liquid crystalmolecules 30 a will be described in detail with reference to FIGS. 3A,3B, 3C and 3D.

[0114] When the electric field is generated in the liquid crystal layer30, torque for orienting the axial direction of the liquid crystalmolecule 30 a parallel to the equipotential line EQ is applied to theliquid crystal molecule 30 a having the negative dielectric anisotropy.As shown in FIG. 3A, when an electric field expressed by anequipotential line EQ vertical to the axial direction of a liquidcrystal molecule 30 a is generated, torque is applied to the liquidcrystal molecule 30 a for inclining it in the clockwise direction or inthe counterclockwise direction in the same probability. Accordingly, ina region of the liquid crystal layer 30 disposed between the parallelplate electrodes opposing each other, the torque is applied in theclockwise direction to some liquid crystal molecules 30 a and in thecounterclockwise direction to other liquid crystal molecules 30 a. As aresult, the orientation sometimes may not be smoothly changed inaccordance with a voltage applied through the liquid crystal layer 30.

[0115] When the electric field inclined against the axial direction ofthe liquid crystal molecules 30 a as expressed by the equipotential lineEQ (inclined electric field) is generated at the edge portion EG of theopening 14 a of the present liquid crystal display device 100 as shownin FIG. 2A, a liquid crystal molecule 30 a is inclined, as shown in FIG.3B, in a direction for orienting parallel to the equipotential line EQwith smaller inclination (in the counterclockwise direction in thedrawing). Furthermore, a liquid crystal molecule 30 a positioned in aregion where an electric field expressed by an equipotential line EQvertical to the axial direction is generated is inclined, as shown inFIG. 3C, in the same direction as another liquid crystal molecule 30 apositioned on the inclined portion of the equipotential line EQ so as tomake continuous (match) their orientations. When an electric fieldexpressed by an equipotential line EQ with continuous irregularities asshown in FIG. 3D is applied, liquid crystal molecules 30 a positioned ona flat portion of the equipotential line EQ are oriented in a directionmatching with the orientation direction of other liquid crystalmolecules 30 a positioned on inclined portions of the equipotential lineEQ. Herein, “to be positioned on an equipotential line EQ” means “to bepositioned within an electric field expressed by an equipotential lineEQ”.

[0116] When the change of the orientation starting from the liquidcrystal molecules 30 a positioned on the inclined portion of theequipotential line EQ is proceeded as described above and the stationarystate is attained, the orientation state as schematically shown in FIG.2B is obtained. The liquid crystal molecules 30 a positioned in thevicinity of the center of the opening 14 a are substantially equallyaffected by the orientations of the liquid crystal molecules 30 apositioned at the opposing edge portions EG of the opening 14 a, andhence, they keep the orientation state vertical to the equipotentialline EQ. The liquid crystal molecules 30 a positioned in a region awayfrom the center of the opening 14 a are inclined owing to the influenceof the orientation of the liquid crystal molecules 30 a positioned atthe closer edge portion EG, so as to form inclined orientationsymmetrically about the center SA of the opening 14 a. When thisorientation state is seen from the vertical direction to the displaysurface of the liquid crystal display device 100 (in the verticaldirection to the surfaces of the substrates 11 and 21), the axialdirections of the liquid crystal molecules 30 a are oriented radiallyabout the center of the opening 14 a (not shown). This orientation stateis herein designated as “radially-inclined orientation”. Also, a regionof the liquid crystal layer in which the radially-inclined orientationis obtained about one center is herein designated as a liquid crystaldomain.

[0117] Also in a region corresponding to the unit solid portion 14 b′substantially surrounded with the openings 14 a, a liquid crystal domainwhere the liquid crystal molecules 30 a are in the radially-inclinedorientation state is formed. The liquid crystal molecules 30 apositioned in the region corresponding to the unit solid portion 14 b′are affected by the orientations of the liquid crystal molecules 30 apositioned at the edge portions EG of the openings 14 a, so as to formthe radially-inclined orientation symmetrical about the center SA of theunit solid portion 14 b′ (corresponding to the center of the unitlattice formed by the openings 14 a).

[0118] The radially-inclined orientation obtained in a liquid crystaldomain formed in the unit solid portion 14 b′ and the radially-inclinedorientation obtained in the opening 14 a are continuous, and the liquidcrystal molecules 30 a positioned in these regions are oriented so as tomatch with the orientation of the liquid crystal molecules 30 apositioned at the edge portions EG of the opening 14 a. The liquidcrystal molecules 30 a in the liquid crystal domain formed in theopening 14 a are oriented in the shape of a cone opening upward (towardthe substrate 100 b), and the liquid crystal molecules 30 a in theliquid crystal domain formed in the unit solid portion 14 b′ areoriented in the shape of a cone opening downward (toward the substrate100 a). In this manner, the radially-inclined orientation obtained inthe liquid crystal domain formed in the opening 14 a and theradially-inclined orientation obtained in the liquid crystal domainformed in the unit solid portion 14 b′ are mutually continuous.Therefore, a disclination line (orientation defect) is never formed onthe boundary thereof, resulting in preventing the display quality fromlowering due to the occurrence of a disclination line.

[0119] In order to improve the viewing angle dependency of the displayquality of a liquid crystal display device in all the azimuths, theexisting probabilities of liquid crystal molecules oriented in therespective azimuth directions in each picture element region arepreferably rotationally symmetrical and are more preferably axiallysymmetrical. In other words, all the liquid crystal domains formed inthe entire picture element region are preferably rotationallysymmetrically arranged and more preferably axially symmetricallyarranged. However, it is not necessary to attain the rotation symmetryin the entire picture element region but the liquid crystal layer of thepicture element region is formed as a collection of liquid crystaldomains rotationally symmetrically (or axially symmetrically) arranged(for example, a plurality of liquid crystal domains disposed in thesquare lattice arrangement). Accordingly, all the plurality of openings14 a formed in the picture element region should not be necessarilyrotationally symmetrically arranged in the entire picture element regionas far as they are expressed as a collection of openings rotationallysymmetrically (or axially symmetrically) arranged (for example, aplurality of openings disposed in the square lattice arrangement).Needless to say, the unit solid portions 14 b′ each surrounded with theplural openings 14 a are similarly arranged. Furthermore, since theshape of each liquid crystal domain is also preferably rotationallysymmetrical and more preferably axially symmetrical, the shape of eachof the openings 14 a and the unit solid portions 14 b′ is preferablyrotationally symmetrical and more preferably axially symmetrical.

[0120] In some cases, a sufficient voltage cannot be applied through aportion of the liquid crystal layer 30 in the vicinity of the center ofthe opening 14 a, so that the portion of the liquid crystal layer 30 inthe vicinity of the center of the opening 14 a cannot make contributionto display. In other words, even when the radially-inclined orientationin the portion of the liquid crystal layer 30 in the vicinity of theopening 14 a is slightly disturbed (for example, when the center axis isslightly shifted from the center of the opening 14 a), the displayquality may not be lowered. Accordingly, at least the liquid crystaldomains formed correspondingly to the unit solid portions 14 b′ shouldbe rotationally symmetrically or axially symmetrically arranged.

[0121] As described with reference to FIGS. 2A and 2B, the pictureelement electrode 14 of the liquid crystal display device 100 of thisinvention has a plurality of openings 14 a, and the electric fieldsexpressed by the equipotential line EQ having the inclined portions areformed in the liquid crystal layer 30 within the picture element region.The liquid crystal molecules 30 a disposed in the liquid crystal layer30 and having the negative dielectric anisotropy, which are in thevertical orientation state when no voltage is applied, are changed intheir orientation directions by being triggered by the orientationchange of the liquid crystal molecules 30 a positioned on the inclinedportions of the equipotential line EQ, so as to form the liquid crystaldomains having the stable radially-inclined orientation in the openings14 a and the solid portion 14 b. The display is produced by changing theorientations of the liquid crystal molecules within the liquid crystaldomains in accordance with the voltage applied through the liquidcrystal layer.

[0122] The shape (seen from the substrate normal direction) and thearrangement of the openings 14 a of the picture element electrode 14 ofthe liquid crystal display device 100 of this embodiment will now bedescribed.

[0123] The display characteristic of a liquid crystal display deviceexhibits azimuth angle dependency derived from the orientation state(optical anisotropy) of liquid crystal molecules. In order to reduce theazimuth angle dependency of the display characteristic, the liquidcrystal molecules are preferably oriented in the respective azimuthangles in equivalent probabilities. Furthermore, the liquid crystalmolecules within each picture element region are preferably oriented inthe respective azimuth angles in equivalent probabilities. Accordingly,the opening 14 a preferably has such a shape that the liquid crystaldomains can be formed so as to orient the liquid crystal molecules 30 ain each picture element region in the respective azimuth angles inequivalent probabilities. Specifically, the shape of the opening 14 a ispreferably rotationally symmetrical (preferably with a rotation axis oftwo or more folds) having its center (along the normal line) as asymmetry axis, and the plural openings 14 a are preferably arranged soas to be rotationally symmetrical. Also, the shape of the unit solidportion 14 b′ substantially surrounded with the openings is preferablyrotationally symmetrical, and the unit solid portions 14 b′ arepreferably arranged so as to be rotationally symmetrical.

[0124] However, it is not necessary to arrange the openings 14 a and theunit solid portions 14 b′ so as to be rotationally symmetrical all overthe picture element region, but when, for example, a square lattice(symmetrical with a four-fold rotation axis) is used as a minimum unitso as to form a picture element region from the combination of thesquare lattices as is shown in FIG. 1A, the liquid crystal molecules canbe oriented in all the azimuth angles in substantially equivalentprobabilities in the entire picture element region.

[0125] The orientation state of the liquid crystal molecules 30 aobtained when the rotationally symmetrical star-shaped openings 14 a andthe substantially circular unit solid portions 14 b are disposed in thesquare lattice arrangement as shown in FIG. 1A will now be describedwith reference to FIGS. 4A, 4B and 4C.

[0126]FIGS. 4A, 4B and 4C schematically show the orientation states ofthe liquid crystal molecules 30 a seen from the substrate normaldirection. In a drawing for showing the orientation state of the liquidcrystal molecules 30 a seen from the substrate normal direction likeFIGS. 4B and 4C, a black end of each liquid crystal molecule 30 a drawnin the shape of an ellipse means that the liquid crystal molecule 30 ais inclined so that the black end be closer to the substrate where thepicture element electrode 14 having the openings 14 a is formed than theother end. This also applies to other drawings mentioned below. Herein,one unit lattice (formed by the four openings 14 a) within the pictureelement region shown in FIG. 1A will be described. The cross-sectionalviews of FIGS. 4A, 4B and 4C taken along their diagonals respectivelycorrespond to FIGS. 1B, 2A and 2B, which are also referred to in thefollowing description.

[0127] When the picture element electrode 14 and the counter electrode22 have the same potential, namely, when no voltage is applied throughthe liquid crystal layer 30, the liquid crystal molecules 30 acontrolled in their orientation direction by the vertical alignmentfilms (not shown) provided on the faces of the TFT substrate 100 a andthe counter substrate 100 b facing the liquid crystal layer 30 are inthe vertical orientation state as shown in FIG. 4A.

[0128] When the electric field expressed by the equipotential line EQ ofFIG. 2A is generated by applying a voltage through the liquid crystallayer 30, the torque is applied to the liquid crystal molecules 30 ahaving the negative dielectric anisotropy so that their axial directionscan be parallel to the equipotential line EQ. As described withreference to FIGS. 3A and 3B, in a liquid crystal molecule 30 apositioned in the electric field expressed by an equipotential line EQvertical to the molecular axis of the liquid crystal molecule 30 a, thedirection for inclining (rotating) the liquid crystal molecule 30 a isnot uniquely determined (as shown in FIG. 3A), and hence, theorientation change (inclination or rotation) cannot be easily caused. Incontrast, in a liquid crystal molecule 30 a positioned on anequipotential line EQ inclined against the molecular axis of the liquidcrystal molecule 30 a, the inclination (rotation) direction is uniquelydetermined, and hence, the orientation change is easily caused.Accordingly, as shown in FIG. 4B, the liquid crystal molecules 30 astart to incline from the edge portions of the openings 14 a where themolecular axes of the liquid crystal molecules 30 a are inclined againstthe equipotential line EQ. Then, as described with reference to FIG. 3C,the liquid crystal molecules 30 a positioned around the inclined liquidcrystal molecules 30 a at the edge portions of the openings 14 a arealso inclined so as to match their orientations. As a result, the axialdirections of the liquid crystal molecules 30 a become stable in a stateas shown in FIG. 4C (in the radially-inclined orientation).

[0129] In this manner, when the opening 14 a has the rotationallysymmetrical shape, the liquid crystal molecules 30 a within the pictureelement region are inclined from the edge portions of the opening 14 atoward the center of the opening 14 a by applying a voltage. Therefore,the liquid crystal molecules 30 a positioned in the vicinity of thecenter of the opening 14 a, where the orientation-regulating forces forthe liquid crystal molecules 30 a working from the respective edgeportions are balanced, are kept to be vertically oriented, with theliquid crystal molecules 30 a positioned around continuously inclinedradially around the liquid crystal molecules 30 a positioned in thevicinity of the center of the opening 14 a.

[0130] Also, the liquid crystal molecules 30 a positioned in the regioncorresponding to the substantially circular unit solid portion 14 b′surrounded with the substantially star-shaped four openings 14 adisposed in the square lattice arrangement are inclined so as to matchtheir orientations with the orientation of the liquid crystal molecules30 a inclined owing to the inclined electric fields generated at theedge portions of the opening 14 a. The liquid crystal molecules 30 apositioned in the vicinity of the center of the unit solid portion 14b′, where the orientation-regulating forces for the liquid crystalmolecules 30 a working from the edge portions are balanced, keep theirvertical orientation to the substrate surface, with the liquid crystalmolecules 30 a positioned around continuously inclined radially aroundthe liquid crystal molecules 30 a positioned in the vicinity of thecenter of the unit solid portion 14 b′.

[0131] When the liquid crystal domains in which the liquid crystalmolecules 30 a are in the radially-inclined orientation state aredisposed in the square lattice arrangement in the entire picture elementregion in this manner, the existing probability of the axial directionsof the liquid crystal molecules 30 a is rotationally symmetrical, andhence, a high quality display free from unevenness can be realized inall the viewing directions. In order to reduce the viewing angledependency of the liquid crystal domain with the radially-inclinedorientation, the liquid crystal domain is preferably highly rotationallysymmetrical (with a rotation axis preferably of two or more folds andmore preferably of four or more folds). Furthermore, in order to reducethe viewing angle dependency of the entire picture element region, theplural liquid crystal domains formed in the picture element region arepreferably disposed in arrangement (of, for example, a square lattice)expressed by a combination of a unit (of, for example, a unit lattice)that is highly rotationally symmetrical (with a rotation axis preferablyof two or more folds and more preferably of four or more folds).

[0132] The radially-inclined orientation of the liquid crystal molecules30 a is more stable when it is clockwise or counterclockwise spiralradially-inclined orientation as shown in FIGS. 5B and 5C than when itis simple radially-inclined orientation as shown in FIG. 5A. In suchspiral orientation, the orientation directions of the liquid crystalmolecules 30 a are not spirally changed along the thickness direction ofthe liquid crystal layer 30 as in the general twist orientation but theorientation directions of the liquid crystal molecules 30 a areminimally changed along the thickness direction of the liquid crystallayer 30 when seen in a small region. Specifically, in a cross-sectiontaken in any position along the thickness direction of the liquidcrystal layer 30 (in any cross-section on a plane parallel to the layersurface), the orientation is the same as that of FIG. 5B or 5C and twistchange along the thickness direction of the liquid crystal layer 30 isminimally caused. However, in the entire liquid crystal domain, thetwist change is caused to some extent.

[0133] When a chiral agent is added to the nematic liquid crystalmaterial having the negative dielectric anisotropy, the liquid crystalmolecules 30 a attain the counterclockwise or clockwise spiralradially-inclined orientation as shown in FIG. 5B or 5C around thecenter of the opening 14 a or the unit solid portion 14 b′ under voltageapplication. The spiral direction depends upon the kind of chiral agentto be used. Accordingly, by placing the liquid crystal layer 30 withinthe opening 14 in the spiral radially-inclined orientation state undervoltage application, the spiral direction of the radially inclinedliquid crystal molecules, 30 a around the liquid crystal molecules 30 aoriented vertically to the substrate surface can be made the same in allthe liquid crystal domains, resulting in realizing even display freefrom unevenness. Furthermore, since the spiral direction around theliquid crystal molecules 30 a oriented vertically to the substratesurface is thus determined, the response speed in applying a voltagethrough the liquid crystal layer 30 can be improved.

[0134] When a chiral agent is added, the orientation of the liquidcrystal molecules 30 a can be spirally changed along the thicknessdirection of the liquid crystal layer 30 as in the general twistorientation. In an orientation state where the orientation of the liquidcrystal molecules 30 a is not spirally changed along the thicknessdirection of the liquid crystal layer 30, liquid crystal molecules 30 aoriented vertically or parallel to the polarization axis of a polarizingplate do not cause a phase difference in incident light, and hence,incident light passing through a region in such an orientation statemakes no contribution to the transmittance. In contrast, in theorientation state where the orientation of the liquid crystal molecules30 a is spirally changed along the thickness direction of the liquidcrystal layer 30, also liquid crystal molecules 30 a oriented verticallyor parallel to the polarization axis of the polarizing plate cause aphase difference in incident lights and the optical activity of thelight can be utilized. Accordingly, the incident light passing through aregion in such an orientation state can make contribution to thetransmittance, resulting in realizing a liquid crystal display devicecapable of bright display.

[0135] Although the opening 14 a is in the substantially star-shape andthe unit solid portion 14 b′ is in the substantially circular shape andthey are disposed in the square lattice arrangement in FIG. 1A, theshapes and the arrangement of the opening 14 a and the unit solidportion 14 b′ are not limited to those shown in FIG. 1A.

[0136]FIGS. 6A and 6B are top views of picture element electrodes 14Aand 14B having openings 14 a and unit solid portions 14 b′ in differentshapes.

[0137] The openings 14 a and the unit solid portions 14 b′ of thepicture element electrodes 14A and 14B shown in FIGS. 6A and 6B are inthe shapes slightly strained as compared with the opening 14 a and theunit solid portion 14 b′ shown in FIG. 1A. The openings 14 a and theunit solid portions 14 b′ of the picture element electrodes 14A and 14Bhave a two-fold rotation axis (not a four-fold rotation axis) and areregularly arranged so as to form a rectangular unit lattice. Eachopening 14 a is in a strained star-shape, and each unit solid portion 14b′ is in an elliptical shape (strained circular shape). Also when any ofthe picture element electrodes 14A and 14B is used, a liquid crystaldisplay device with high display quality and a good viewing anglecharacteristic can be obtained.

[0138] Furthermore, any of picture element electrodes 14C and 14Drespectively shown in FIGS. 7A and 7B may be used.

[0139] In each of the picture element electrodes 14C and 14D, openings14 a each in substantially a cross-shape are disposed in a squarelattice arrangement so as to form a unit solid portion 14 b′ insubstantially a square shape. Needless to say, they may be strained andarranged to form a rectangular unit lattice. Also when such unit solidportions 14 b′ in a substantially rectangular shape (including a squareshape) are thus regularly arranged, a liquid crystal display devicehaving high display quality and a good viewing angle characteristic canbe obtained.

[0140] However, the opening 14 a and/or the unit solid portion 14 b′ arepreferably in a circular or elliptical shape as compared with arectangular shape because the radially-inclined orientation can bestabilized when they are circular or elliptical. This is probablybecause the edge portions of the openings 14 a are continuously(smoothly) changed when they are circular or elliptical so that theorientation directions of the liquid crystal molecules 30 a can becontinuously (smoothly) changed.

[0141] From the viewpoint of the aforementioned continuity of theorientation directions of the liquid crystal molecules 30 a, any ofpicture element electrodes 14E and 14F respectively shown in FIGS. 8Aand 8B may be used. The picture element electrode 14E of FIG. 8A is amodification of the picture element electrode 14 of FIG. 1A and has anopening 14 a formed from four arcs alone. The picture element electrode14F of FIG. 8B is a modification of the picture element electrode 14D ofFIG. 7B and has an opening 14 a having arc-shaped edges adjacent to unitsolid portions 14 b′. The opening 14 a and the unit solid portion 14 b′of each of the picture element electrodes 14E and 14F have a four-foldrotation axis and are disposed in the square lattice arrangement (with afour-fold rotation axis). However, the opening 14 a and the unit solidportion 14 b′ may be strained to have a two-fold rotation axis anddisposed in rectangular lattice arrangement (with a two-fold rotationaxis) as shown in FIGS. 6A and 6B.

[0142] In the aforementioned examples, the opening 14 a is formed in thesubstantially star-shape or the substantially cross-shape, and the unitsolid portion 14 b′ is formed in the substantially circular shape, thesubstantially elliptical shape, the substantially square (rectangular)shape or the substantially rectangular shape with round corners. Incontrast, the relationship between the opening 14 a and the unit solidportion 14 b′ may be negatively/positively reversed. For example, FIG. 9shows a picture element electrode 14G having a pattern obtained bynegatively/positively reversing the pattern of the opening 14 a and theunit solid portion 14 b of the picture element electrode 14 of FIG. 1A.The picture element electrode 14G having such a negatively/positivelyreversed pattern can exhibit substantially the same function as thepicture element electrode 14 of FIG. 1. In the case where the opening 14a and the unit solid portion 14 b′ are both in a substantially squareshape as in picture element electrodes 14H and 14I respectively shown inFIGS. 10A and 10B, a negatively/positively reversed pattern is the sameas the original pattern.

[0143] Also in the pattern of FIG. 9 obtained by negatively/positivereversing the pattern of FIG. 1A, some (approximately a half or aquarter) of the opening 14 a are preferably formed at the edge portionsof the picture element electrode 14 so as to form a rotationallysymmetrical unit solid portion 14 b′. Thus, the effect derived from theinclined electric field can be obtained also at the edges of the pictureelement region similarly to the center of the picture element region, soas to realize stable radially-inclined orientation in the entire pictureelement region.

[0144] Now, it will be described whether a negative pattern or apositive pattern should be employed by exemplifying the picture elementelectrode 14 of FIG. 1A and the picture element electrode 14G of FIG. 9having the pattern obtained by negatively/positively reversing thepattern of the opening 14 a and the unit solid portion 14 b′ of thepicture element electrode 14.

[0145] In either of the negative and positive patterns, the length ofthe edges of the opening 14 a is the same. Accordingly, there is nodifference between these patterns in the function to generate theinclined electric field. However, the area ratio of the unit solidportions 14 b′ (the ratio to the entire area of the picture elementelectrode 14) may be different in these patterns. Specifically, thepatterns may be different in the area of a solid portion 14 b (where theconducting film actually exists) for generating the electric fieldapplied to the liquid crystal molecules of the liquid crystal layer.

[0146] A voltage applied to a liquid crystal domain formed in theopening 14 a is lower than a voltage applied to a liquid crystal domainformed in the solid portion 14 b. Therefore, for example, in normallyblack mode display, the liquid crystal domain formed in the opening 14 ais darker. In other words, as the area ratio of the opening 14 a ishigher, the display luminescence tends to be lowered. Accordingly, thearea ratio of the solid portion 14 b is preferably higher.

[0147] It depends upon the pitch (size) of the unit lattice in which ofthe pattern of FIG. 1A and the pattern of FIG. 9 the area ratio of thesolid portion 14 b is higher.

[0148]FIG. 11A shows the unit lattice of the pattern of FIG. 1A, andFIG. 11B shows the unit lattice (whereas having the opening 14 a as thecenter) of the pattern of FIG. 9. In FIG. 11A, portions for mutuallyconnecting the adjacent unit solid portions 14 b′ (namely, branchportions extending in the four directions from the circular portion) inFIG. 1 are omitted. It is herein assumed that the length (pitch) of oneside of the square unit lattice is p and that the length of spacebetween the opening 14 a or the unit solid portion 14 b′ and the unitlattice (side space) is s.

[0149] A variety of picture element electrodes 14 respectively havingdifferent pitches p and different side spaces s are fabricated, so as toexamine the stability of the radially-inclined orientation and the like.As a result, it is first found that, in order to generate an inclinedelectric field necessary for attaining the radially-inclined orientationby using a picture element electrode 14 having the pattern of FIG. 11A(hereinafter referred to as the positive pattern), the side space sshould be approximately 2.75 μm or more. On the other hand, with respectto a picture element electrode 14 having the pattern of FIG. 11B(hereinafter referred to as the negative pattern), it is found that theside space s should be approximately 2.25 μm or more for generating theinclined electric field for attaining the radially-inclined orientationwith the side spaces s set to these lower limit values, the area ratiosof the solid portion 14 b obtained by varying the value of the pitch pare examined. The results are shown in Table 1 and FIG. 11C. TABLE 1Area ratio of solid portion (%) Pitch p (μm) Positive pattern Negativepattern 20 41.3 52.9 25 47.8 47.2 30 52.4 43.3 35 55.8 40.4 40 58.4 38.245 60.5 36.4 50 62.2 35.0

[0150] As is understood from Table 1 and FIG. 1C, when the pitch p isapproximately 25 μm or more, the area ratio of the solid portion 14 b ishigher in the positive pattern (shown in FIG. 11A), and when the pitch pis smaller than approximately 25 μm, the area ratio of the solid portion14 b is higher in the negative pattern (shown in FIG. 11B). Accordingly,from the viewpoint of the display luminescence and the stability oforientation, the pattern to be employed is changed depending uponwhether the pitch p is larger than or smaller than approximately 25 μm.For example, in the case where three or less unit lattices are formed inthe lateral direction of a picture element electrode 14 with a width of75 μm, the positive pattern as shown in FIG. 11A is preferred, and inthe case where four or more unit lattices are formed, the negativepattern as shown in FIG. 11B is preferred. In employing any of thepatterns other than the exemplified patterns of FIGS. 11A and 11B, apositive pattern or a negative pattern is appropriately selected so asto attain a higher area ratio of the solid portion 14 b.

[0151] The number of unit lattices is obtained as follows: The size of aunit lattice is calculated so that one, two or a larger integral numberof unit lattices can be arranged along the width or length of thepicture element electrode 14. The area ratio of a solid portion iscalculated with respect to each size of the unit lattice, so as toselect the unit lattice size for maximizing the area ratio of the solidportion. However, the orientation-regulating force obtained by theinclined electric field is degraded and the stable radially-inclinedorientation is difficult to attain when the diameter of the unit solidportion 14 b′ is smaller than 15 μm in employing a positive pattern andwhen the diameter of the opening 14 a is smaller than 15 μm in employinga negative pattern. The lower limit values of these diameters areobtained when the liquid crystal layer 30 has a thickness ofapproximately 3 μm. In the case where the liquid crystal layer 30 has asmaller thickness, the stable radially-inclined orientation can beattained even when the diameter of the unit solid portion 14 b′ or theopening 14 a is smaller than the lower limit value. In the case wherethe liquid crystal layer 30 has a larger thickness, the lower limit;value of the diameter of the unit solid portion 14 b′ or the opening 14a required for attaining the stable radially-inclined orientation islarger than the aforementioned lower limit value.

[0152] As described in detail in Embodiment 2 below, the stability ofthe radially-inclined orientation can be improved by forming aprotrusion within the opening 14 a. The aforementioned conditions areapplied when no protrusion is formed.

[0153] With respect to the positive pattern as shown in FIG. 11A, avariety of picture element electrodes 14 respectively having differentshapes of the unit solid portion 14 b′ and different side spaces s arefabricated, so as to examine the stability of the radially-inclinedorientation and the transmittance. Also, the orientation stabilityobtained by changing the cell thickness (the thickness of the liquidcrystal layer 30) is also examined. In the examinations described below,a liquid crystal display device of a normally black mode equipped with a18.1-inch SXGA panel is used.

[0154] First, picture element electrodes 14 including unit solidportions 14 b′ respectively in the shapes as shown in FIGS. 12A, 12B,12C and 12D are evaluated for their orientation stability with the pitchp set to 42.5 μm, the side space s set to 4.25 μm, 3.50 μm or 2.75 μmand the cell thickness set to 3.70 μm or 4.15 μm. In the 18.1-inch SXGApanel, the unit lattices can be most efficiently arranged (withoutwasting any area of the picture element region) when the pitch p is 42.5μm.

[0155]FIG. 12A is a diagram for schematically showing the unit latticeof a picture element electrode 14 having a unit solid portion 14 b′ in asubstantially circular shape, FIGS. 12B and 12C are diagrams forschematically showing the unit lattices of picture element electrodes 14each having a unit solid portion 14 b′ in a substantially square shapewith substantially arc-shaped corners, and FIG. 12D is a diagram forschematically showing the unit lattice of a picture element electrode 14including a unit solid portion 14 b′ in a substantially square shape.The unit solid portions of FIGS. 12B and 12C are different from eachother in the ratio between a radius r of curvature approximatelyexpressing the shape of the substantially arc-shaped corner and a lengthL of one side of the unit solid portion, which is 1:3 in FIG. 12B and1:4 in FIG. 12C. In FIGS. 12A, 12B, 12C and 12D, the portions mutuallyconnecting the adjacent unit solid portions 14 b′ in FIG. 1 (the branchportions extending toward the four directions from the circular portion)are omitted.

[0156] The degree of the orientation stability can be evaluated by, forexample, examining the presence of a residual image in displaying adynamic image. In displaying a dynamic image in which a black box ismoving with a intermediate gray scale background, the degree of theorientation stability tends to affect the display. When the degree ofthe orientation stability is comparatively low, a white tailing residualimage may occur. This white tailing residual image may be caused when anematic liquid crystal material including a chiral agent is used as theliquid crystal material. The cause of the occurrence of the whitetailing residual image will be described later.

[0157] Table 2 shows the results of visual evaluation of the degree ofoccurrence of the white tailing residual image obtained with theaforementioned various parameters varied. In Table 2, the shapes of theunit solid portions 14 b′ respectively shown in FIGS. 12A, 12B, 12C and12D are designated as a circle, a barrel A, a barrel B and a square.Also, in Table 2, ⊚ denotes that the tailing residual image is notobserved, ◯ denotes that the tailing residual image is minimallyobserved and Δ denotes that the tailing residual image is observed.TABLE 2 Side spaces (μm) 4.25 3.50 2.75 Cell thickness (μm) 3.70 4.153.70 4.15 3.70 4.15 Circle ⊚ ⊚ ⊚ ⊚ ⊚ ◯ Barrel A ⊚ ⊚ Δ Δ Δ Δ Barrel B ⊚ ⊚Δ Δ Δ Δ Square ⊚ Δ Δ Δ Δ Δ

[0158] As shown in Table 2, with respect to the shape of the unit solidportion 14 b′, the orientation stability is higher in the order of thecircle, the barrel A, the barrel B and the square. This is because thecontinuity in the orientation direction of the liquid crystal molecules30 a in the radially-inclined orientation state is higher as the shapeof the unit solid portion 14 b′ is more approximate to a circle. Also asshown in Table 2, the orientation stability is higher as the side spaces is larger. This is because the effect to control the orientation bythe inclined electric field is more remarkably exhibited as the sidespace s is larger. Furthermore, the orientation stability is higher asthe cell thickness is smaller. This is because the effect to control theorientation by the inclined electric field is more remarkably exhibitedas the cell thickness is smaller.

[0159] In order to evaluate the orientation stability, the degree ofoccurrence of unevenness through pressure (pressure residual image) isalso evaluated. As a result, it is confirmed that the orientationstability is higher as the cell thickness is smaller. The pressureresidual image is evaluated by examining the degree at which orientationturbulence caused by applying a stress to the panel surface of theliquid crystal display device remains as display unevenness afterremoving the stress.

[0160] Next, the transmittance is evaluated with the various parametersvaried as in the evaluation of the orientation stability. Table 3 showsthe results of the transmittance measured in white display (underapplication of a voltage of 6.0 V through the liquid crystal layer) in aliquid crystal display device with a cell thickness of 3.70 μm. Table 3shows transmittance ratios calculated by assuming that the transmittanceof a liquid crystal display device using a picture element electrode 14including a unit solid portion 14 b′ in the shape of the barrel B andhaving a side space s of 4.25 μm is 1. Also, a parenthesized numericalvalue in Table 3 is an actually measured value of the transmittance(namely, the front transmittance obtained by assuming that the lightintensity of a backlight source in white display is 100). TABLE 3 Sidespace s (μm) 4.25 3.50 2.75 Circle 0.885 0.917 0.940 (3.06)  (3.17) (3.25)  Barrel A 0.953 0.989 1.024 (3.29)  (3.42)  (3.54)  Barrel B1.000 1.031 (3.45)  (3.56)  Square 1.028 (3.55) 

[0161] As shown in Table 3, with respect to the shape of the unit solidportion 14 b′, the transmittance is higher in the order of the square,the barrel B, the barrel A and the circle. This is because, when theside space s is the same, the area ratio of the solid portion 14 b ishigher as the shape of the unit solid portion 14 b′ is more approximateto a square, and hence, the area (defined on a plane seen from thesubstrate normal direction) of a portion of the liquid crystal layerdirectly affected by the electric fields generated by the electrodes islarger, resulting in increasing the effective aperture ratio. Also asshown in Table 3, the transmittance is higher as the side space s issmaller. This is because as the side space s is smaller, the area ratioof the solid portion 14 b is higher, and hence, the effective apertureratio is higher.

[0162] As described above, the orientation stability is higher as theshape of the unit solid portion 14 b′ is more approximate to a circleand as the side space s is larger. Also, the orientation stability ishigher as the cell thickness is smaller.

[0163] Furthermore, since the effective aperture ratio is higher as thearea ratio of the solid portion 14 b is higher, the transmittance ishigher as the shape of the unit solid portion 14 b′ is more approximateto a square (or a rectangle) and as the side space s is smaller.

[0164] Accordingly, in consideration of desired orientation stabilityand transmittance, the shape of the unit solid portion 14 b′, the sidespace s and the cell thickness are determined.

[0165] When the unit solid portion 14 b′ is in a substantially squareshape with substantially arc-shaped corners as shown in FIGS. 12B and12C, both the orientation stability and the transmittance can becomparatively high. Needless to say, the aforementioned effect can beattained when the unit solid portion 14 b′ is in a substantiallyrectangular shape with substantially arc-shaped corners. The corner ofthe unit solid portion 14 b′ formed from a conducting film may not be inan arc-shape precisely due to the restriction in fabrication process butmay be in an obtuse-angled polygonal shape (a shape formed from aplurality of angles exceeding 90 degrees). The corner may be formed notonly in the shape of a quarter arc or a regular polygonal shape (forexample, a part of a regular polygon) but also in the shape of aslightly strained arc (such as a part of an ellipse) or a strainedpolygonal shape. Alternatively, the corner may be in a shape obtained bycombining a curve and an obtuse angle. The substantially arc-shapedcorner herein includes corners in any of the aforementioned shapes. Forthe same reason in the production process, also in the unit solidportion 14 b′ in the substantially circular shape as shown in FIG. 12A,the shape may not be a precise circle but may be a polygonal shape or aslightly strained circle.

[0166] In the liquid crystal display devices whose orientation stabilityand transmittance are listed in Tables 2 and 3, both the orientationstability and the transmittance can be comparatively high in using apicture element electrode 14 including a unit solid portion in the shapeof the barrel B and having a side space s of 4.25 μm.

[0167] The structure of the liquid crystal display device ofEmbodiment 1. is substantially the same as that of a conventionalvertical alignment type liquid crystal display device except that thepicture element electrode 14 is an electrode having the openings 14 a,and the present liquid crystal display device can be fabricated by anyof the known fabrication methods.

[0168] In order to vertically orient the liquid crystal molecules havingthe negative dielectric anisotropy, the vertical alignment layers (notshown) are typically formed on the faces of the picture elementelectrode 14 and the counter electrode 22 facing the liquid crystallayer 30.

[0169] As the liquid crystal material, a nematic liquid crystal materialhaving the negative dielectric anisotropy is used. Also, a liquidcrystal display device of a guest-host mode may be fabricated by addinga dichroic pigment. A liquid crystal display device of a guest-host modedoes not require a polarizing plate.

Embodiment 2

[0170] The structure of one picture element region of a liquid crystaldisplay device 200 according to Embodiment 2 of the invention will nowbe described with reference to FIGS. 13A and 13B. In all the drawingsreferred to below, like reference numerals are used to refer to likeelements having substantially the same functions as those of the liquidcrystal display device 100, so as to omit the description. FIG. 13A is atop view seen from the substrate normal direction, and FIG. 13B is across-sectional view taken along line 13B-13 B′ of FIG. 13A. FIG. 13Bshows a state where no voltage is applied through the liquid crystallayer.

[0171] As shown in FIGS. 13A and 13B, the liquid crystal display device200 is different from the liquid crystal display device 100 ofEmbodiment 1 shown in FIGS. 1A and 1B in a TFT substrate 200 a includinga protrusion 40 within each opening 14 a of the picture elementelectrode 14. On the protrusion 40, a vertical alignment film (notshown) is provided.

[0172] The cross-sectional structure of the protrusion 40 taken along aplane direction of the substrate 11 is the same as the shape of theopening 14 a as is shown in FIG. 13A, and is herein a substantiallystar-shape. The adjacent protrusions 40 are mutually connected, so as tocompletely surround the unit solid portion 14 b′ substantiallycircularly. The cross-sectional structure of the protrusion 40 takenvertically to the plane direction of the substrate 11 is in atrapezoidal shape as shown in FIG. 13B. Specifically, the protrusion hasa top face 40 t parallel to the substrate surface and side faces 40 sinclined at a taper angle θ (<90°) against the substrate face. Since thevertical alignment film (not shown) is formed so as to cover theprotrusion 40, the side face 40 s of the protrusion 40 hasorientation-regulating force for orienting the liquid crystal molecules30 a of the liquid crystal layer 30 in the same direction as theorientation-regulating direction of the inclined electric field, so asto stabilize the radially-inclined orientation.

[0173] This function of the protrusion 40 will now be described withreference to FIGS. 14A, 14B, 14C, 14D, 15A and 15B.

[0174] First, the relationship between the orientation of a liquidcrystal molecule 30 a and the shape of a face having a verticalalignment property will be described with reference to FIGS. 14A, 14B,14C and 14D.

[0175] As shown in FIG. 14A, a liquid crystal molecule 30 a positionedon a horizontal face is oriented vertically to the face by theorientation-regulating force of the face having the vertical alignmentproperty (typically, a surface of a vertical alignment film). When anelectric field expressed by an equipotential line EQ vertical to theaxial direction of the liquid crystal molecule 30 a is applied to thisvertically oriented liquid crystal molecule 30 a, torque is applied tothe liquid crystal molecule 30 a for inclining it in the clockwisedirection or in the counterclockwise direction in equivalentprobabilities. Accordingly, in the liquid crystal layer 30 disposedbetween parallel plate type electrodes opposing each other, the torqueis applied in the clockwise direction to some liquid crystal molecules30 a and in the counterclockwise direction to other liquid crystalmolecules 30 a. As a result, the change to the orientation state inaccordance with the voltage applied through the liquid crystal layer 30sometimes may not be smoothly caused.

[0176] As shown in FIG. 14B, when the electric field expressed by ahorizontal equipotential line EQ is applied to a liquid crystalmolecules 30 a oriented vertically to an inclined face, the liquidcrystal molecule 30 a is inclined in a direction for orienting parallelto the equipotential line EQ with smaller inclination (in the clockwisedirection in the drawing). Furthermore, as shown in FIG. 14C, a liquidcrystal molecule 30 a oriented vertically to the horizontal face isinclined in the same direction (the clockwise direction) as anotherliquid crystal molecule 30 a positioned on the inclined face so as tomake continuous (match) their orientations.

[0177] As shown in FIG. 14D, on an irregular face whose cross-section isin a continuous trapezoidal shape, liquid crystal molecules 30 apositioned on the top or lower horizontal faces are oriented so as tomatch with the orientation directions of liquid crystal molecules 30 apositioned on the inclined faces.

[0178] In the liquid crystal display device of this embodiment, theradially-inclined orientation is stabilized by making theorientation-regulating direction obtained by such a face shape(protrusion) accord with the orientation-regulating direction obtainedby the inclined electric field.

[0179]FIGS. 15A and 15B show states obtained by applying a voltagethrough the liquid crystal layer 30 of FIG. 13B, and specifically, FIG.15A schematically shows the state where the orientation of the liquidcrystal molecules 30 a starts to change in accordance with the voltageapplied through the liquid crystal layer 30 (the ON initial state) andFIG. 15B schematically shows the state where the orientation of theliquid crystal molecules 30 a changed in accordance with the appliedvoltage attains the stationary state. In FIGS. 15A and 15B, a line EQdenotes an equipotential line.

[0180] When the picture element electrode 14 and the counter electrode22 have the same potential (namely, when no voltage is applied throughthe liquid crystal layer 30), the liquid crystal molecules 30 a withinthe picture element region are oriented vertically to the faces of thesubstrates 11 and 21 as shown in FIG. 13B. At this point, a liquidcrystal molecule 30 a in contact with the vertical alignment film (notshown) formed on the side face 40 s of the protrusion 40 is orientedvertically to the side face 40 s, and a liquid crystal molecule 30 a inthe vicinity of the side face 40 s is oriented to be inclined as shownin the drawing due to the interaction (property as an elastic substance)with the liquid crystal molecules 30 a around.

[0181] When a voltage is applied through the liquid crystal layer 30,potential gradient expressed by the equipotential line EQ of FIG. 15A isformed. The equipotential line EQ is parallel to the faces of the solidportion 14 b and the counter electrode 22 within a region of the liquidcrystal layer 30 positioned between the solid portion 14 b of thepicture element electrode 14 and the counter electrode 22 and drops in aregion corresponding to the opening 14 a of the picture elementelectrode 14, and an inclined electric field expressed by an inclinedportion of the equipotential line EQ is formed in a region of the liquidcrystal layer 30 at the edge portion of the opening 14 a (the insideperiphery of the opening 14 a including the boundary).

[0182] Owing to this inclined electric field, a liquid crystal molecule30 a positioned on the edge portion EG is inclined (rotated) in theclockwise direction at the edge portion EG on the right hand side in thedrawing and in the counterclockwise direction at the edge portion EG onthe left hand side in the drawing as described above, so as to orientparallel to the equipotential line EQ. The orientation-regulatingdirection by this inclined electric field accords with theorientation-regulating direction obtained by the side face 40 spositioned at each edge portion EG.

[0183] As described above, when the change of the orientation startingfrom the liquid crystal molecules 30 a positioned on the inclinedportions of the equipotential line EQ is proceeded to attain thestationary state, the orientation state schematically shown in FIG. 15Bis obtained. The liquid crystal molecules 30 a positioned in thevicinity of the center of the opening 14 a, namely, in the vicinity ofthe top face 40 t of the protrusion 40, are affected substantiallyequally by the orientations of the liquid crystal molecules 30 apositioned at the opposing edge portions EG of the opening 14 a, andhence keep the orientation vertical to the equipotential line EQ. Theliquid crystal molecules 30 a positioned away from the center of theopening 14 a (namely, the top face 40 t of the protrusion 40) areinclined due to the influence of the orientation of the liquid crystalmolecules 30 a positioned at the closer edge portion EG, so as to formthe inclined orientation symmetrical about the center SA of the opening14 a (the top face 40 t of the protrusion 40). Also, in a regioncorresponding to the unit solid portion 14 b′ substantially surroundedby the openings 14 a and the protrusion 40, the inclined orientationsymmetrical about the center SA of the unit solid portion 14 b′ isformed.

[0184] In this manner, also in the liquid crystal display device 200 ofEmbodiment 2, liquid crystal domains having the radially-inclinedorientation are formed correspondingly to the openings 14 a and the unitsolid portions 14 b′ in the same manner as in the liquid crystal displaydevice 100 of Embodiment 1. Since the protrusion 40 is formed so as tocompletely surround the unit solid portion 14 b′ substantiallycircularly, a liquid crystal domain is formed correspondingly to thesubstantially circular region surrounded by the protrusion 40.Furthermore, the side face of the protrusion 40 formed within theopening 14 a works to incline the liquid crystal molecules 30 apositioned in the vicinity of the edge portion EG of the opening 14 a inthe same direction as the orientation direction caused by the inclinedelectric field, resulting in stabilizing the radially-inclinedorientation.

[0185] Naturally, the orientation-regulating force obtained by theinclined electric field works merely under application of voltage anddepends upon the magnitude of the electric field (i.e., the magnitude ofthe applied voltage). Accordingly, when the electric field has smallmagnitude (namely, when the applied voltage is low), theorientation-regulating force by the inclined electric field is weak, andhence, the radially-inclined orientation may be destroyed due tofloating of the liquid crystal material when an external force isapplied to the liquid crystal panel. Once the radially-inclinedorientation is destroyed, the radially-inclined orientation cannot berestored until a voltage sufficiently high for generating the inclinedelectric field exhibiting sufficiently strong orientation-regulatingforce is applied. In contrast, the orientation-regulating force by theside face 40 s of the protrusion 40 works regardless of the appliedvoltage and is very strong as is known as an anchoring effect of analignment film. Accordingly, even when the radially-inclined orientationis once destroyed due to the floating of the liquid crystal material,the liquid crystal molecules 30 a positioned in the vicinity of the sideface 40 s of the protrusion 40 keep their orientation directions thesame as those in the radially-inclined orientation. Therefore, theradially-inclined orientation can be easily restored when the floatingof the liquid crystal material is stopped.

[0186] In this manner, the liquid crystal display device 200 ofEmbodiment 2 has not only the same characteristic as that of the liquidcrystal display device 100 of Embodiment 1 but also a characteristic ofhigh resistance against an external force. Accordingly, the liquidcrystal display device 200 is suitably used in a PC or PDA generallyused as portable equipment to which an external force is frequentlyapplied.

[0187] When the protrusion 40 is formed from a dielectric substance withhigh transparency, the protrusion 40 can advantageously increase thecontribution to display of a liquid crystal domain formedcorrespondingly to the opening 14 a. On the other hand, when theprotrusion 40 is formed from an opaque dielectric substance, lightleakage derived from retardation of the liquid crystal molecules 30 aoriented to be inclined owing to the side face 40 s of the protrusion 40can be advantageously prevented. It can be determined depending upon theapplication of the liquid crystal display device which type ofdielectric substance is used. In either case, when the dielectricsubstance is a photosensitive resin, a step of patterning the dielectricsubstance in accordance with the pattern of the openings 14 a can beadvantageously simplified. In order to attain sufficientorientation-regulating force, the height of the protrusion 40 ispreferably within a range between approximately 0.5 μm and approximately2 μm when the liquid crystal layer 30 has a thickness of approximately 3μm. In general, the height of the protrusion 40 is preferably in a rangebetween approximately ⅙ through approximately ⅔ of the thickness of theliquid crystal layer 30.

[0188] As described above, the liquid crystal display device 200includes the protrusion 40 within the opening 14 a of the pictureelement electrode 14, and the side face 40 s of the protrusion 40 hasthe orientation-regulating force for orienting the liquid crystalmolecules 30 a of the liquid, crystal layer 30 in the same direction asthe orientation-regulating direction obtained by the inclined electricfield. Preferable conditions for the side face 40 s to attain theorientation-regulating force in the same direction as theorientation-regulating direction of the inclined electric field will nowbe described with reference to FIGS. 16A, 16B and 16C.

[0189]FIGS. 16A, 16B and 16C are schematic cross-sectional views ofliquid crystal display devices 200A, 200B and 200C, respectively, all ofwhich correspond to FIG. 15A. All of the liquid crystal display devices200A, 200B and 200C have the protrusions within the openings 40 a andare different from the liquid crystal display device 200 in thepositional relationship between the entire protrusion 40 as a singlestructure and the opening 14 a.

[0190] In the aforementioned liquid crystal display device 200, theentire protrusion 40 as a single structure is formed within the opening14 a and the bottom of the protrusion 40 is smaller than the opening 14a as shown in FIG. 15A. In the liquid crystal display device 200A ofFIG. 16A, the bottom of the protrusion 40A accords with the opening 14a, and in the liquid crystal display device 200B of FIG. 16B, theprotrusion 40B has a bottom larger than the opening 14 a so that theprotrusion 40B covers a part of the solid portion (conducting film) 14 baround the opening 14 a. In each of the protrusions 40, 40A and 40B, thesolid portion 14 b is not formed on the side face 40 s. As a result, theequipotential line EQ is substantially flat on the solid portion 14 band drops in the opening 14 a as shown in the respective drawings.Accordingly, the side face 40 s of each of the protrusions 40A and 40Bof the liquid crystal display devices 200A and 200B can exhibit theorientation-regulating force in the same direction as theorientation-regulating direction of the inclined electric fieldsimilarly to the protrusion 40 of the liquid crystal display device 200,so as to stabilize the radially-inclined orientation.

[0191] In contrast, the bottom of the protrusion 40C of the liquidcrystal display device 200C of FIG. 16C is larger than the opening 14 a,and a part of the solid portion 14 b around the opening 14 a is formedon the side face 40 s of the protrusion 40C. Owing to the solid portion14 b formed on the side face 40 s, a crest is formed in theequipotential line EQ. The crest of the equipotential line EQ has agradient reverse to that of the equipotential line EQ dropping in theopening 14 a, which means that an inclined electric field is generatedin the reverse direction to the inclined electric field for orientingthe liquid crystal molecules 30 a to be radially inclined. Accordingly,in order to attain the side face 40 s exhibiting theorientation-regulating force in the same direction as theorientation-regulating direction of the, inclined electric field, it ispreferred that the solid portion (conducting film) 14 b is not formed onthe side face 40 s.

[0192] Next, the cross-sectional structure of the protrusion 40 takenalong line 17A-17A′ of FIG. 13A will be described with reference to FIG.17.

[0193] Since the protrusion 40 of FIG. 13A is formed so as to completelysurround the unit solid portion 14 b′ substantially circularly asdescribed above, the portions for mutually connecting the adjacent unitsolid portions 14 b′ (the branch portions extending in the fourdirections from the circular portion) are formed on the protrusion 40 asshown in FIG. 17. Accordingly, there is a risk of disconnection causedon the protrusion 40 in depositing the conducting film for forming thesolid portion 14 b of the picture element electrode 14, or peeling maybe highly probably caused in a subsequent step of the fabricationprocess.

[0194] Therefore, as in a liquid crystal display device 200D shown inFIGS. 18A and 18B, an independent protrusion 40D is formed to becompletely contained within the opening 14 a. Thus, the conducting filmfor forming the solid portion 14 b is formed on the flat surface of thesubstrate 11, and hence, the risk of disconnection and peeling can beavoided. Although the protrusion 40D is not formed so as to completelysurround the unit solid portion 14 b′ substantially circularly, a liquidcrystal domain in the substantially circular shape is formedcorrespondingly to the unit solid portion 14 b′, so as to stabilize theradially-inclined orientation similarly to the aforementioned liquidcrystal display device.

[0195] The effect to stabilize the radially-inclined orientation byforming the protrusion 40 in the opening 14 a is exhibited not only inthe opening 14 a having the aforementioned pattern but also in theopening 14 a having any of the patterns described in Embodiment 1, andthe same effect can be attained in employing any of the patterns. Inorder to sufficiently exhibit the effect to stabilize theradially-inclined orientation against an external force by theprotrusion 40, the pattern (seen from the substrate normal direction) ofthe protrusion 40 preferably has a shape for surrounding a region of theliquid crystal layer 30 as large as possible. Accordingly, the effect tostabilize the orientation by the protrusion 40 can be more remarkablyexhibited in a positive pattern, for example, having a circular unitsolid portion 14 b′ than in a negative pattern having a circular opening14 a.

Arrangement of Polarizing Plate and Phase Plate

[0196] In the so-called vertical alignment type liquid crystal displaydevice including a liquid crystal layer in which liquid crystalmolecules having the negative dielectric anisotropy are verticallyoriented under application of no voltage, a display can be produced in avariety of display modes. For example, not only a birefringence mode forproducing a display by controlling the birefringence of the liquidcrystal layer with an electric field but also an optical rotating modeand a combination of the optical rotating mode and the birefringencemode can be employed as the display mode. When a pair of polarizingplates are provided on the outside of the pair of substrates (forexample, the TFT substrate and the counter substrate) in each of theliquid crystal display devices described in Embodiments 1 and 2, aliquid crystal display device of the birefringence mode can be obtained.Also, a phase compensating device (typically, a phase plate) may beprovided if necessary. Furthermore, a liquid crystal display devicecapable of bright display can be obtained by using substantiallycircularly polarized light.

[0197] In the liquid crystal display device in which the liquid crystaldomains are placed in the spiral radially-inclined orientation state asshown in FIGS. 5B and 5C, the display quality can be further improved byoptimizing the positions of the polarizing plates. Now, preferredpositions of the polarizing plates will be described. Herein, thedescription will be given by exemplifying a liquid crystal displaydevice for producing a display in the normally black mode in which apair of polarizing plates are provided on the outside of a pair ofsubstrates (for example, a TFT substrate and a counter substrate) so asto have their polarization axes substantially perpendicularly to eachother. The spiral radially-inclined orientation state is realized byusing, for example, a nematic liquid crystal material having thenegative dielectric anisotropy including a chiral agent. In thefollowing description, the “spirally radially-inclined orientation” issometimes simply referred to as “spiral orientation”.

[0198] First, the orientation states of liquid crystal moleculesobtained when liquid crystal domains are in the spiral orientation statewill be described with reference to FIGS. 19A, 19B and 19C. FIG. 19A isa diagram for schematically showing the orientation state of the liquidcrystal molecules obtained immediately after applying a voltage throughthe liquid crystal layer, and FIGS. 19B and 19C are diagrams forschematically showing the orientation state of the liquid crystalmolecules obtained in the orientation stable time (stationary state).

[0199] Immediately after applying a voltage through the liquid crystallayer, the liquid crystal molecules 30 a are placed in a simpleradially-inclined orientation state in a plurality of liquid crystaldomains as shown in FIG. 19A. When the orientation is further proceededthereafter, the liquid crystal molecules 30 a are inclined inpredetermined directions on the plane of the liquid crystal layer, andin the orientation stable time (stationary state), the liquid crystalmolecules 30 a are in the clockwise or counterclockwise spiralorientation as shown in FIG. 19B or 19C.

[0200] At this point, when the liquid crystal molecules 30 a areinclined in the counterclockwise direction, the liquid crystal domain isin the clockwise spiral orientation state as shown in FIG. 19B, and whenthe liquid crystal molecules 30 a are inclined in the clockwisedirection, the liquid crystal domain is in the counterclockwise spiralorientation state as shown in FIG. 19C. The direction of the spiralorientation depends upon, for example, the kind of chiral agent added tothe liquid crystal material.

[0201] The degree of inclination of the liquid crystal molecules 30 a onthe plane is regulated, as shown in FIGS. 19B and 19C, by an angle θagainst the 12 o'clock direction on the display surface (that is, theupper direction of the display surface and also simply referred to asthe 12 o'clock direction) of a liquid crystal molecule 30 a′ positionedin the 12 o'clock direction on the display surface in regard to thecenter of each of the plural liquid crystal domains. The center of theliquid crystal domain typically substantially accords with the center ofthe opening or the solid portion.

[0202] The liquid crystal molecule 30 a′ disposed in the aforementionedposition may actually be inclined at an angle different from the angleθ. Herein, the inclination angles of liquid crystal molecules 30 a′disposed in the aforementioned position against the 12 o'clock directionon the display surface and the existing probabilities of the liquidcrystal molecules 30 a′ are examined, so as to define the inclinationangle of the liquid crystal molecule 30 a′ with the highest probabilityas the angle θ. Typically, the inclination angle of a liquid crystalmolecule 30 a, positioned in the vicinity of the center in the thicknessdirection of the liquid crystal layer substantially accords with theangle θ. The angle of a liquid crystal molecule 30 a, against the 12o'clock direction is, strictly speaking, an angle between the azimuthdirection of the orientation direction of the liquid crystal molecule 30a′ and the 12 o'clock direction.

[0203] In the liquid crystal display device in which the liquid crystaldomains are in the spiral orientation state as described above, thelight transmittance obtained when the liquid crystal domains are in thespiral orientation state can be improved when a pair of polarizingplates are disposed so that the polarization axis of one polarizingplate can be inclined in the same direction as the inclination of theaforementioned liquid crystal molecule by an angle exceeding 0 degreebut smaller than 2θ against the 12 o'clock direction. Thus, brightdisplay can be obtained. Now, this will be described in more detail byusing examples.

[0204] First, with reference to FIG. 20, description will be given onthe change of transmittance obtained by changing the inclination angleof the polarization axis against the 12 o'clock direction by rotatingthe pair of polarizing plates kept in a crossed Nicols state about theliquid crystal panel in white display state, namely, in the state wherethe liquid crystal domains are in the spiral radially-inclinedorientation state under application of a predetermined voltage throughthe liquid crystal layer. FIG. 20 is a graph having the ordinateindicating the transmittance in the white display state of a liquidcrystal display device including a liquid crystal layer (with athickness of 3.8 μm) formed from a liquid crystal material with a chiralpitch of 16 μm and the abscissa indicating the angle of the polarizationaxis against the 12 o'clock direction. In this case, the transmittanceobtained when the angle of the polarization axis against the 12 o'clockdirection is 0 degree is assumed as 100%. Also, the liquid crystalmolecules of the liquid crystal layer included in this liquid crystaldisplay device are in the clockwise spiral orientation state as shown inFIG. 19B in the orientation stable time, and the liquid crystal moleculepositioned in the 12 o'clock direction is inclined in thecounterclockwise direction by approximately 13 degrees, against the 12o'clock direction (namely, θ≈13°). In drawings referred to in thefollowing description, this liquid crystal display device (namely, theliquid crystal display device in which the liquid crystal molecules arein the clockwise spiral orientation state in the orientation stable timeand the liquid crystal molecule positioned in the 12 o'clock directionis inclined in the counterclockwise direction by approximately 13degrees against the 12 o'clock direction) is shown unless otherwisementioned.

[0205] As shown in FIG. 20, the transmittance is increased as thepolarization axis is inclined in the counterclockwise direction againstthe 12 o'clock direction and is the maximum when the angle of thepolarization axis against the 12 o'clock direction is approximately 13degrees (namely, θ). When the polarization axis is further inclined, thetransmittance is lowered, and when the angle of the polarization axisagainst the 12 o'clock direction is approximately 26 degrees (namely,2θ), the transmittance becomes equal to that obtained when the angle is0 degree. When the angle exceeds 26 degrees, the transmittance becomeslower than that obtained when the angle is 0 degree.

[0206] The light transmittance is changed as described above because thearea of shade regions of the liquid crystal domain changes in accordancewith the inclination angle of the polarization axis against the 12o'clock direction. The shade region corresponds to a region defined byliquid crystal molecules oriented vertically or parallel to thepolarization axis, and the liquid crystal layer in the shade regionminimally causes a phase difference in incident light. Accordingly, theincident light passing through the shade region makes littlecontribution to the transmittance. Therefore, the transmittance obtainedwhen the liquid crystal domain is in the spiral orientation statedepends upon the area of the shade region. The transmittance is lower asthe area of the shade region is larger, and the transmittance is higheras the area of the shade region is smaller.

[0207] The change of the shade region in accordance with the inclinationangle of the polarization axis will now be described with reference toFIGS. 21A, 21B, 22A and 22B. FIGS. 21A and 21B are diagrams forschematically showing shade regions SR of a liquid crystal domainobtained when the polarization axis is parallel to the 12 o'clockdirection, and FIGS. 22A and 22B are diagrams for schematically showingshade regions SR obtained when the polarization axis is inclined byapproximately 13 degrees against the 12 o'clock direction.

[0208] When the polarization axis is parallel to the 12 o'clockdirection as shown in FIG. 21A, the shade regions SR are observed indirections shifted in the clockwise direction respectively from the 12o'clock direction, the 3 o'clock direction, the 6 o'clock direction andthe 9 o'clock direction in regard to the center of the liquid crystaldomain. In contrast, when the polarization axis is inclined byapproximately 13 degrees against the 12 o'clock direction as shown inFIG. 22A, the shade regions SR are observed in the 12 o'clock direction,the 3 o'clock direction, the 6 o'clock direction and the 9 o'clockdirection in regard to the center of the liquid crystal domain.

[0209] When the area of the shade regions SR obtained when thepolarization axis is parallel to the 12 o'clock direction as shown inFIG. 21B is assumed to be S1 and the area of the shade regions SRobtained when the polarization axis is inclined by approximately 13degrees (namely, θ) against the 12 o'clock direction is assumed to beS2, the area S1 is larger than the area S2 (S1>S2). This is because theexisting probability of liquid crystal molecules oriented vertically orparallel to the polarization axis is lower in the case where thepolarization axis is inclined by approximately 13 degrees against the 12o'clock direction than in the case where the polarization axis isparallel to the 12 o'clock direction.

[0210] In this manner, assuming that the liquid crystal moleculepositioned in the 12 o'clock direction in regard to the center of theliquid crystal domain is inclined from the 12 o'clock direction by theangle θ, the polarizing plates are disposed so that the polarizationaxis of one of the polarizing plates can be inclined from the 12 o'clockdirection by the angle exceeding 0 degree and smaller than 2θ in thesame direction as the inclination direction of the liquid crystalmolecule. Thus, the existing probability of the liquid crystal moleculesoriented vertically or parallel to the polarization axis is lower thanin the case where the polarization axis is parallel to the 12 o'clockdirection. Accordingly, the light transmittance obtained when the liquidcrystal domain is in the spiral radially-inclined orientation state canbe improved by disposing the polarizing plates in the aforementionedmanner, resulting in realizing bright display.

[0211] Furthermore, when the polarizing plates are disposed so that thepolarization axis of one polarizing plate can be inclined atsubstantially the same angle as the angle θ as shown in FIG. 22A, theshade regions SR are positioned in the 12 o'clock direction, the 3o'clock direction, the 6 o'clock direction and the 9 o'clock directionin regard to the center of the liquid crystal domain as shown in FIG.22B. As a result, the existing probability of the liquid crystalmolecules oriented vertically or parallel to the polarization axis canbe further lowered. Therefore, when the polarizing plates are thusdisposed, the light transmittance can be further increased, resulting inrealizing further bright display.

[0212] In the above description, the preferable arrangement of thepolarizing plates is described from the viewpoint of the improvement inthe transmittance. Furthermore, when the pair of polarizing plates arearranged so that the polarization axis of one of the polarizing platescan be inclined in the same direction as the inclination of theaforementioned liquid crystal molecule by an angle exceeding 0 degreeand smaller than θ against the 12 o'clock direction, not only brightdisplay can be realized but also occurrence of a white tailingphenomenon (a phenomenon in which a white tailing residual image isobserved) and a black tailing phenomenon (a phenomenon in which a blacktailing residual image is observed) described below can be suppressed,resulting in realizing display with high quality.

[0213] The white tailing phenomenon may occur, for example, in the casewhere an image of a black box moving with a intermediate gray scalebackground is displayed in a liquid crystal display device. FIG. 23 is adiagram for schematically showing the white tailing phenomenon. When animage where a black box is moving in the rightward direction with aintermediate gray scale background as shown in FIG. 23 is displayed, aregion with higher luminescence than the intermediate gray scale isformed on the left hand side of the black box so as to be observed as awhite tailing residual image.

[0214] The white tailing phenomenon comparatively easily occurs when,for example, the polarization axis is parallel to the 12 o'clockdirection. In contrast, for example, in the liquid crystal displaydevice whose transmittance change is shown in FIG. 20, when thepolarizing plates are arranged so that the polarization axis can beinclined by approximately 13 degrees against the 12 o'clock direction,the white tailing phenomenon can be prevented from occurring indisplaying the image where the black box is moving in the rightwarddirection with the intermediate gray scale background as shown in FIG.24.

[0215] The reason will be described with reference to FIGS. 25A, 25B,25C, 26A, 26B and 26C. FIGS. 25A, 25B and 25C are diagrams forschematically showing shade regions SR in a liquid crystal domainobtained when the polarization axis of the polarizing plate is parallelto the 12 o'clock direction. FIG. 25A shows the polarization axis of thepolarizing plate, FIG. 25B shows the shade regions SR obtainedimmediately after applying a voltage through the liquid crystal layer,and FIG. 25C shows the shade regions SR obtained in the orientationstable time (stationary state). FIGS. 26A, 26B and 26C are diagrams forschematically showing shade regions SR obtained in a liquid crystaldomain when the polarization axis of the polarizing plate is inclined byapproximately 13 degrees against the 12 o'clock direction. FIG. 26Ashows the polarization axis of the polarizing plate, FIG. 26B shows theshade regions SR obtained immediately after applying a voltage throughthe liquid crystal layer and FIG. 26C shows the shade regions SRobtained in the orientation stable time (stationary state).

[0216] First, the case where the polarization axis of one of the pair ofthe polarizing plates is parallel to the 12 o'clock direction as shownin FIG. 25A will be described. When the polarizing plates are thusarranged, the shade regions SR are observed in the 12 o'clock direction,the 3 o'clock direction, the 6 o'clock direction and the 9 o'clockdirection in regard to the center of the liquid crystal domain as shownin FIG. 25B. Also, in the orientation stable time, the shade regions areobserved in directions shifted in the clockwise direction respectivelyfrom the 12 o'clock direction, the 3 o'clock direction, the 6 o'clockdirection and the 9 o'clock direction in regard to the center of theliquid crystal domain as shown in FIG. 25C.

[0217] When the area of the shade regions SR obtained immediately aftervoltage application shown in FIG. 25B is assumed to be S1′ and the areaof the shade regions SR obtained in the orientation stable time shown inFIG. 25C is assumed to be S1, the area S1 is larger than the area S1′,and the transmittance is higher immediately after the voltageapplication than in the orientation stable time. Therefore, when theimage in which the black box is moving in the rightward direction withthe intermediate gray scale background is displayed as shown in FIG. 23,in picture element regions where the black box has just passed, namely,picture element regions that are being changed from the black displaystate to the intermediate gray scale display state, the transmittance istransiently higher than that obtained in the intermediate gray scalestate (the transmittance obtained in the orientation stable time). As aresult, this transiently high transmittance is observed as a whitetailing residual image.

[0218] In contrast, when the polarizing plates are disposed so that thepolarization axis of one polarizing plate be inclined by approximately13 degrees against the 12 o'clock direction as shown in FIG. 26A, theshade regions SR are observed in directions shifted in thecounterclockwise direction respectively from the 12 o'clock direction,the 3 o'clock direction, the 6 o'clock direction and the 9 o'clockdirection in regard to the center of the liquid crystal domain as shownin FIG. 26B in the simple radially-inclined orientation state attainedimmediately after the voltage application. Alternatively, in theorientation stable time, the shade regions SR are observed in the 12o'clock direction, the 3 o'clock direction, the 6 o'clock direction andthe 9 o'clock direction in regard to the center of the liquid crystaldomain as shown in FIG. 26C.

[0219] When the area of the shade regions SR obtained immediately afterthe voltage application shown in FIG. 26B is assumed to be S2′ and thearea of the shade regions SR obtained in the orientation stable timeshown in FIG. 26C is assumed to be S2, the area S2 is smaller than thearea S2′, and the transmittance is higher in the orientation stable timethan immediately after the voltage application. Furthermore, when thepolarizing plates are thus arranged, the transmittance is the highest inthe orientation stable time. Therefore, when the image where the blackbox is moving in the rightward direction with the intermediate grayscale background is displayed as shown in FIG. 24, in picture elementregions where the black box has just passed, namely, picture elementregions that are being changed from the black display state to theintermediate gray scale display state, the transmittance never becomestransiently higher than the transmittance of the intermediate gray scalestate (the transmittance obtained in the orientation stable time). As aresult, the occurrence of the white tailing phenomenon can be definitelyprevented in the liquid crystal display device in which the polarizingplates are thus arranged.

[0220]FIG. 27 shows change with time of the transmittance obtained bychanging a given picture element region from the black display state tothe intermediate gray scale display state when the polarization axis isparallel to the 12 o'clock direction and when the polarization axis isinclined by approximately 13 degrees against the 12 o'clock direction.In this graph, the transmittance obtained in the intermediate gray scaledisplay state is assumed to be 1.00 and the time when a voltage isapplied through the liquid crystal layer of this picture element regionis assumed to be 0 sec.

[0221] In the case where the polarization axis is parallel to the 12o'clock direction, the transmittance largely exceeds 1.00 immediatelyafter the voltage application and becomes predetermined transmittance(the transmittance of the intermediate gray scale display state)thereafter as shown with a solid line in FIG. 27. Therefore, when thepolarizing plates are thus arranged, the white tailing phenomenon mayoccur.

[0222] In contrast, in the case where the polarization axis is inclinedby approximately 13 degrees against the 12 o'clock direction, thetransmittance never largely exceeds 1.00 immediately after the voltageapplication as shown with a dashed line in FIG. 27. Therefore, theoccurrence of the white tailing phenomenon can be definitely preventedwhen the polarizing plates are thus arranged.

[0223] In the above description, the case where the polarization axis isinclined by approximately 13 degrees (namely, the angle θ) against the12 o'clock direction is described as an example of the arrangement ofthe polarizing plates for preventing the occurrence of the white tailingphenomenon. When the polarizing plates are thus arranged, thetransmittance is the highest in the orientation stable time as describedabove, and hence, the occurrence of the white tailing phenomenon can bedefinitely prevented.

[0224] However, the arrangement for preventing the occurrence of thewhite tailing phenomenon is not limited to the aforementionedarrangement for attaining the highest transmittance in the orientationstable time. Alternatively, the occurrence of the white tailingphenomenon can be suppressed when the polarizing plates are arranged sothat a difference between transient highest transmittance and thetransmittance obtained in the orientation stable time can be smallerthan that in the case where the polarization axis is parallel to the 12o'clock direction.

[0225] For example, when the polarization axis is inclined in the samedirection as the inclination direction of the liquid crystal molecule byan angle exceeding 0 degree and equal to θ or less against the 12o'clock direction, the occurrence of the white tailing phenomenon can besuppressed, resulting in realizing display with high quality. Also, whenthe polarization axis is inclined within the aforementioned range, notonly the occurrence of the white tailing phenomenon can be suppressedbut also the transmittance obtained in the orientation stable time canbe increased, resulting in realizing bright display. Within theaforementioned range, as the inclination angle of the polarization axisis larger, the white tailing phenomenon can be further suppressed. Whenthe polarization axis is inclined by an angle substantially equal toθ/2, the occurrence of the white tailing phenomenon can be substantiallyavoided.

[0226] The arrangement for suppressing the occurrence of the whitetailing phenomenon is not limited to the aforementioned arrangement, anddepending upon the arrangement of the polarizing plates, the change ofthe transmittance caused in changing a picture element region from theblack display state to the intermediate gray scale display state is tooslow to cause a black tailing phenomenon.

[0227] The black tailing phenomenon occurs, similarly to the whitetailing phenomenon, for example, in displaying an image where a blackbox is moving with the intermediate gray scale background in a liquidcrystal display device. FIG. 28 is a diagram for schematically showingthe black tailing phenomenon. As shown in FIG. 28, when the image wherethe black box is moving in the rightward direction with the intermediategray scale background is displayed, a region with higher luminescencethan the black display state but lower luminescence than theintermediate gray scale display state is formed on the left hand side ofthe black box, so as to be observed as a black tailing residual image.

[0228] The black tailing phenomenon comparatively easily occurs when thepolarization axis of the polarizing plate is inclined at an angleexceeding θ against the 12 o'clock direction. For example, when thepolarization axis is inclined by approximately 20 degrees against the 12o'clock direction, the change of the transmittance from the blackdisplay state to the intermediate gray scale display state is too slowas schematically shown with a two-dot chain line in FIG. 27. Therefore,in displaying the image where the black box is moving as describedabove, picture element regions where the black box has just passedcannot rapidly attain the intermediate gray scale display state, whichmay result in the black tailing phenomenon.

[0229] For example, when the polarization axis is inclined in the samedirection as the inclination direction of the liquid crystal molecule byan angle exceeding 0 degree and smaller than θ against the 12 o'clockdirection, the occurrence of the black tailing phenomenon can besuppressed, resulting in realizing display with high quality. Also, whenthe polarization axis is inclined within the aforementioned range, notonly the occurrence of the black tailing phenomenon is suppressed butalso the transmittance obtained in the orientation stable time can beincreased, resulting in realizing bright display. When the inclinationangle of the polarization axis is the angle exceeding 0 degree and equalto θ or less against the 12 o'clock direction and in the same directionas the inclination direction of the liquid crystal molecule, the blacktailing phenomenon can be further suppressed as the inclination angle ofthe polarization axis is smaller. When the polarization axis is inclinedby an angle substantially the same as θ/2, the occurrence of the blacktailing phenomenon can be substantially avoided.

[0230] The occurrence of the white tailing phenomenon and the blacktailing phenomenon can be suppressed by optimizing the arrangement ofthe polarizing plates as described above. From the viewpoint ofsuppressing the occurrence of the tailing phenomenon and improvement ofthe transmittance, the pair of polarizing plates are preferably arrangedso that the polarization axis of one polarizing plate can be inclined inthe same direction as the inclination direction of the liquid crystalmolecule by the angle exceeding 0 degree and equal to θ or less. Whenthe polarizing plates are thus arranged, bright display can be realizedand the occurrence of the tailing phenomenon (including the whitetailing phenomenon and the black tailing phenomenon) can be suppressed,resulting in realizing display with high quality. Furthermore, when thepolarizing plates are arranged so that the polarization axis of onepolarizing plate is inclined by an angle substantially the same as θ/2,the occurrence of the white tailing phenomenon and the black tailingphenomenon can be substantially avoided, resulting in realizing displaywith higher quality.

[0231] The spiral orientation of the liquid crystal domain can beobtained by using a liquid crystal material including a chiral agent asdescribed above. At this point, there are cases where the orientation ofthe liquid crystal molecules is spirally changed along the thicknessdirection of the liquid crystal layer in accordance with the amount ofchiral agent to be added and where such spiral orientation change isminimally caused. In either case, the display quality can be improved byoptimizing the arrangement of the polarizing plates as described above.

Width and Number of Branch Portions

[0232] As described above, the picture element electrode 14 of theliquid crystal display device 100 or 200 of this invention includes aplurality of openings 14 a and a solid portion 14 b. A unit solidportion 14 b′ disposed within a unit lattice formed by the openings 14 ais typically electrically connected to an adjacent unit solid portion 14b′. Portions for electrically connecting the adjacent unit solidportions 14 b′, for example, branch portions extending toward fourdirections from the circular portion as shown in FIG. 1A naturallyreceive the same potential as another portion of the unit solid portion,and hence, these branch portions also affect the orientation-regulatingeffect obtained by the inclined electric field.

[0233] As shown in FIG. 29, the solid portion 14 b typically includes aplurality of island portions 14 c and a plurality of branch portions 14d for electrically connecting adjacent pairs of the island portions 14c. Herein, the island portion 14 c corresponds to a portion of theconducting film positioned within a unit lattice excluding the branchportions 14 d.

[0234] Liquid crystal molecules of a region of the liquid crystal layer30 positioned on the island portion 14 c are controlled in theirorientation by the inclined electric field generated on a boundarybetween the island portion 14 c and the opening 14 a (namely, the edgeportion of the opening 14 a). In order to realize a stable orientationstate and a good response characteristic, the inclined electric fieldfor controlling the orientation of the liquid crystal molecules 30 ashould be made to work on a large number of liquid crystal molecules 30a, and for this purpose, the boundaries between the island portions 14 cand the openings 14 a are preferably formed in a large number.

[0235] When the branch portions 14 d are present between the islandportions 14 c as shown in FIG. 29, the number of boundaries between theisland portions 14 c and the openings 14 a is reduced owing to thebranch portions 14 d, and hence, the number of edge portions where theinclined electric fields for controlling the orientation of the liquidcrystal molecules 30 a disposed on the island portions 14 c is reduced.In other words, the branch portion 14 d present between the islandportions 14 c degrades the orientation-regulating effect derived fromthe inclined electric field. Accordingly, as the width of each branchportion 14 d is smaller or as the number of branch portions 14 d issmaller, the degradation of the orientation-regulating effect can befurther suppressed so as to improve the response characteristic.

[0236] Also, since the inclined electric field is generated on theboundary between the branch portion 14 d and the opening 14 a, theliquid crystal molecules 30 a positioned on the branch portion 14 d arecontrolled in their orientation. The orientation of the liquid crystalmolecules 30 a positioned on the branch portion 14 d also affects theorientation state of liquid crystal molecules 30 a positioned on theisland portion 14 c, resulting in affecting the response characteristic.This will now be described in more detail.

[0237] First, with reference to FIGS. 30 and 31, the orientation stateof a region of the liquid crystal layer 30 positioned on the islandportion 14 c will be described. FIG. 30 is a schematic top view of theorientation state of the liquid crystal molecules 30 a under voltageapplication, and FIG. 31 is a cross-sectional view thereof taken alongline 31A-31A′ or 31B-31 B′ of FIG. 30. In a liquid crystal displaydevice shown in these drawings, the island portion 14 c is formed in abarrel shape (a square with arc-shaped corners), a liquid crystalmaterial including a chiral agent is used, and the liquid crystal layer30 is in a spiral radially-inclined orientation state. Also in thisliquid crystal display device, a bowl-shaped protrusion (a protrusionhaving one spherical face) 24 for fixing the center of theradially-inclined orientation in the vicinity of the center of the unitsolid portion 14 b′ and improving the orientation stability is formed onthe counter electrode 22 provided on the counter substrate 100 b asshown in FIG. 31, but the following description does not differ evenwhen such a protrusion 24 is not provided.

[0238] As shown in FIG. 30, when a voltage is applied through the liquidcrystal layer 30, the orientation directions of the liquid crystalmolecules 30 a are regulated by the inclined electric fieldsrespectively generated on the boundaries between the openings 14 a andthe island portions 14 c (the edge portions of the openings 14 a), sothat the region of the liquid crystal layer 30 positioned on each islandportion 14 c is placed in the spiral radially-inclined orientationstate.

[0239] In a cross-section taken along a direction where no branchportion 14 d exists as in the cross-section taken along line 31A-31A′ or31B-31B′ of FIG. 30, orientation-regulating force for inclining all theliquid crystal molecules 30 a from the edge portions of the opening 14 atoward the center of the island portion 14 c works as shown in FIG. 31.In the case where the island portion 14 c is formed in a circular shape,the strength of the orientation-regulating force is the same in anycross-sections taken along directions where no branch portion 14 dexists. However, in the case where the island portion 14 c is in thebarrel shape as shown in FIG. 30, the strength of theorientation-regulating force depends upon the distance between thecenter of the island portion 14 c and the edge portion.

[0240] In this manner, the region of the liquid crystal layer 30positioned on the island portion 14 c is stably placed in the spiralradially-inclined orientation state having its orientation center in thevicinity of the center of the island portion 14 c under the voltageapplication. This state is herein designated as a first stable state forsimplifying the following description.

[0241] Next, with reference to FIGS. 32 and 33, the orientation state ofa region of the liquid crystal layer 30 positioned on the opening 14 awill be described. FIG. 32 is a schematic top view of the orientationstate of the liquid crystal molecules 30 a under voltage application,and FIG. 33 is a cross-sectional view thereof taken along line 33A-33A′or 33B-33B′ of FIG. 32.

[0242] In a cross-section along a direction where no branch portion 14 dexists as in the cross-section taken along line 33A-33A′ or 33B-33 B′ ofFIG. 32, orientation-regulating force for inclining all the liquidcrystal molecules 30 a from the edge portions of the opening 14 a towardthe center of the opening 14 a works as shown in FIG. 33. However, theliquid crystal molecules 30 a of the region of the liquid crystal layer30 positioned on the opening 14 a are not directly affected by theelectric fields generated by the electrodes, and hence, they areinclined at an angle smaller than the inclination angle of the liquidcrystal molecules 30 a positioned on the island portion 14 c.

[0243] In this manner, the region of the liquid crystal layer 30positioned on the opening 14 a are stably placed in theradially-inclined orientation state having its orientation center in thevicinity of the opening 14 a under the voltage application.

[0244] Subsequently, with reference to FIGS. 34, 35A and 35B, theorientation state of a region of the liquid crystal layer 30 positionedon the branch portion 14 d will be described. FIG. 34 is a schematic topview of the orientation state of the liquid crystal molecules 30 a undervoltage application, FIG. 35A is a cross-sectional view thereof takenalong line 35A-35A′ of FIG. 34, and FIG. 35B is a cross-sectional viewthereof taken along line 35B-35B′ of FIG. 34.

[0245] In a cross-section taken along a direction crossing the boundarybetween the branch portion 14 d and the opening 14 a as in thecross-section taken along line 35A-35A′ of FIG. 34, the orientationdirections of the liquid crystal molecules 30 a are regulated by theinclined electric field generated on the boundary between the branchportion 14 d and the opening 14 a as shown in FIG. 35A. On the otherhand, in a cross-section taken along a direction crossing the branchportion 14 d and the island portion 14 c as in the cross-section takenalong line 35B-35B′ of FIG. 34, the liquid crystal molecules 30 a areinclined so as to match with the orientation state of the region of theliquid crystal layer 30 positioned on the adjacent island portion 14 cas shown in FIG. 35B.

[0246] Accordingly, the liquid crystal molecules 30 a of the region ofthe liquid crystal layer 30 positioned on the branch portion 14 d areoriented, as shown in FIG. 36, so as to match with the orientation ofthe liquid crystal molecules 30 a positioned on the adjacent islandportion 14 c and the orientation of the liquid crystal molecules 30 apositioned on the opening 14 a (correspondingly to the aforementionedfirst stable state). In FIG. 36, liquid crystal molecules 30 a havingorientation axes along the vertical direction on the display surface(the 12 o'clock direction and the 6 o'clock direction) and thehorizontal direction on the display surface (the 3 o'clock direction andthe 9 o'clock direction) are shown.

[0247] The orientation-regulating force obtained in the section takenalong line 35B-35B′ (that is, very weak orientation-regulating forceworking for keeping continuity in the orientations of surrounding liquidcrystal molecules) is much weaker than the orientation-regulating forceof the inclined electric field generated at the edge portion of theopening 14 a. Furthermore, the inclination direction of the liquidcrystal molecule 30 a obtained by the aforementionedorientation-regulating force is reverse (namely, the liquid crystalmolecules 30 a are oriented in the shape of a cone opening downward(toward the substrate 100 a)) to the inclination direction of the liquidcrystal molecules 30 a obtained by the inclined electric field generatedon the boundary between the branch portion 14 d and the opening 14 a(namely, the liquid crystal molecules 30 a are oriented in the shape ofa cone opening upward (toward the substrate 100 b)). Therefore, balanceof the orientation-regulating forces working on the liquid crystalmolecules 30 a positioned on the branch portion 14 d can be easily lost.

[0248] Accordingly, the liquid crystal molecules 30 a verticallyoriented (namely, the liquid crystal molecules 30 a positioned at theorientation center) in the cross-section along the direction crossingthe boundary between the branch portion 14 d and the opening 14 a(corresponding to the cross-section taken along line 35A-35A′ of FIG.34) tend to move toward the boundary between the branch portion 14 d andthe opening 14 a as shown in FIGS. 37A and 37B.

[0249] Owing to the influence of such a shift of the orientation of theliquid crystal molecules 30 a positioned on the branch portion 14 d(namely, the positional shift of the vertically oriented liquid crystalmolecules 30 a), the spiral orientation of the region of the liquidcrystal layer 30 positioned on the island portion 14 c is changed fromthe first stable state shown in FIG. 36 to a second stable state shownin FIG. 38. This affects the response characteristic of the liquidcrystal display device, so that it can take comparatively long time tostabilize the orientation to attain the stationary state.

[0250] The orientation state of the liquid crystal molecules 30 apositioned on the branch portion 14 d that affects the responsecharacteristic as described above largely depends upon the presence(number) and the width of the branch portions 14 d. When each branchportion 14 d has a comparatively large width as shown in FIG. 39B, thebalance of the orientation-regulating forces working on the liquidcrystal molecules positioned on the branch portion 14 d can be easilylost, so as to largely affect the orientation stable state of the liquidcrystal molecules 30 a positioned on the island portion 14 c. Incontrast, when each branch portion 14 d has a comparatively small widthas shown in FIG. 39A, the orientation-regulating forces are wellbalanced on the liquid crystal molecules 30 a positioned on the branchportion 14 d, so that the orientation state of the liquid crystalmolecules 30 a positioned on the island portion 14 c can also bestabilized comparatively early, resulting in improving the responsecharacteristic of the liquid crystal display device.

[0251] The influence of the width of the branch portion 14 d on theresponse characteristic will be more specifically described withreference to FIG. 40. FIG. 40 is a graph for schematically showingchange with time of transmittance attained by applying a voltage throughthe liquid crystal layer 30 when the branch portion 14 d has acomparatively small width (of, for example, 5.5 μm) and when the branchportion 14 d has a comparatively large width (of, for example, 7.5 μm).In this case, a pair of polarizing plates are provided so as to havetheir polarization axes respectively in parallel to the 12 o'clockdirection and the 3 o'clock direction.

[0252] As described with reference to FIG. 27, in the case where thepolarization axis of the polarizing plate is in parallel to the 12o'clock direction, the transmittance once becomes the maximum (maximumtransmittance Ip of FIG. 40) immediately after the voltage applicationand becomes substantially constant thereafter. The liquid crystal layer30 is once placed in the simple radially-inclined orientation stateimmediately after the voltage application and is changed to the spiralradially-inclined orientation state, and at this point, the orientationpasses through the first stable state shown in FIG. 36 and then attainsthe second stable state shown in FIG. 38.

[0253] As shown in FIG. 40, time Ta necessary for attaining the secondstable state when the branch portion 14 d has a comparatively smallwidth is shorter than time Tb necessary for attaining the second stablestate when the branch portion 14 d has a comparatively large width(Ta<Tb). Thus, as the branch portion 14 d has a smaller width, a betterresponse characteristic can be attained (the response speed is faster).

[0254] Also, transmittance Ia attained in the second stable state whenthe branch portion 14 d has a comparatively small width is higher thantransmittance Ib attained in the second stable state when the branchportion 14 d has a comparatively large width (Ia>Ib).

[0255] The reason will be described with reference to FIGS. 41A and 41B.FIGS. 41A and 41B are diagrams for schematically showing liquid crystalmolecules 30 a oriented in a direction parallel to the polarization axesin the second stable state, and specifically, FIG. 41A shows theorientation obtained when the branch portion 14 d has a comparativelysmall width and FIG. 41B shows the orientation obtained when the branchportion 14 d has a comparative large width. In FIGS. 41A and 41B, arrowsdenote the directions of the polarization axes of the pair of polarizingplates, and in this case, the polarization axes of the polarizing platesare respectively in parallel to the 12 o'clock direction and the 3o'clock direction.

[0256] In the case where the polarizing plates are thus arranged, aregion where the liquid crystal molecules 30 a oriented in the directionparallel to the polarization axes of the polarizing plates exitcorresponds to a shade region for transmitting substantially no light.

[0257] In the case where the branch portion 14 d has a comparativelysmall width, the liquid crystal molecules 30 a oriented in thedirections parallel to the polarization axes are present substantiallyalong the 12 o'clock direction, the 3 o'clock direction, the 6 o'clockdirection and the 9 o'clock direction as shown in FIG. 41A. Therefore,the shade regions are observed substantially along the polarizationaxes. In contrast, in the case where the branch portion 14 d has acomparatively large width, the liquid crystal molecules 30 a oriented inthe directions parallel to the polarization axes are present also inpositions shifted from the 12 o'clock direction, the 3 o'clockdirection, the 6 o'clock direction and the 9 o'clock direction as shownin FIG. 41B. Therefore, the positions where the shade regions areobserved are different from those shown in FIG. 41A.

[0258] The area of the shade regions is the minimum when they areobserved along the polarization axes. Therefore, the area of the shaderegions is smaller in the case where the branch portion 14 d has acomparatively small width as shown in FIG. 41A than in the case wherethe branch portion 14 d has a comparatively large width as shown in FIG.41B. Accordingly, the transmittance attained in the second stable stateis higher in the case where the branch portion 14 d has a comparativelysmall width.

[0259] As described above, the transmittance Ia attained in the secondstable state when the branch portion 14 d has a comparatively smallwidth is higher than the transmittance Ib attained in the second stablestate when the branch portion 14 d has a comparatively large width.Therefore, change AIa of the transmittance between immediately after thevoltage application and the second stable state obtained when the branchportion 14 d has a comparatively small width is smaller than change AIbof the transmittance between immediately after the voltage applicationand the second stable state obtained when the branch portion 14 d has acomparatively large width (AIa<AIb). Accordingly, the white tailingphenomenon as shown in FIG. 23 is less observed when the branch portion14 d has a comparatively small width than when the branch portion 14 dhas a comparatively large width, and hence, a good responsecharacteristic can be attained.

[0260] As described above, as each branch portion 14 d has a smallerwidth, the response characteristic is further improved. Also bycomparatively reducing the number of branch portions 14 d, the responsecharacteristic can be improved.

[0261] In the picture element electrode 14 of the liquid crystal displaydevice of this invention, all the adjacent pairs of island portions 14 cmay be mutually connected by the branch portions 14 d as shown in FIG.42. However, the response characteristic can be improved byappropriately omitting the branch portions 14 d. The picture elementelectrode 14 is connected to a switching element, for example, through acontact hole 19 formed in a shade region 18 of FIG. 42, and therespective island portions 14 c are mutually electrically connectedthrough the branch portions 14 d so as to function as substantially oneconducting film. The shade region 18 corresponds to, for example, aregion on a storage capacitance line on the TFT substrate and is aregion which light from a backlight does not pass through and makes nocontribution to the display.

[0262] Specifically, when the number of branch portions 14 d provided toeach island portion 14 c is, for example, two or less as shown in FIGS.43 and 44, a good response characteristic can be attained.

[0263] A branch portion 14 d positioned in a region making nocontribution to the display such as the shade region 18 minimallyaffects the response characteristic. Therefore, as shown in FIG. 45, thenumber of branch portions 14 d provided to each island portion 14 c in aregion making contribution to the display may be two or less

[0264] Needless to say, the structure of the solid portion 14 b is notlimited to those described above. When the branch portions 14 d arepartly omitted as compared with the structure of FIG. 42 and the islandportions 14 c have redundancy as shown in FIG. 46, a liquid crystaldisplay device having a good response characteristic that can befabricated at a high ratio of acceptable products can be obtained.

[0265] When the number of branch portions 14 d is reduced as comparedwith the case where all the adjacent pairs of island portions 14 c areconnected through the branch portions 14 d as shown in FIG. 42, theresponse characteristic can be improved. The number of branch portions14 d, namely, how many branch portions 14 d are omitted, can bedetermined in accordance with a desired response characteristic.

[0266] For example, in the case where the plural island portions 14 care arranged in the form of an m×n matrix (wherein m and n are naturalnumbers of 2 or more), if all the adjacent island portions 14 c areconnected through the branch portions 14 d, the number of branchportions 14 d is (2mn−m−n). Accordingly, in the case where the islandportions 14 c are arranged in the form of the m×n matrix, the responsecharacteristic can be improved when the number of branch portions issmaller than (2mn−m−n).

[0267] When the width and the number of branch portions 14 d areoptimized as described above, a good response characteristic can beattained.

[0268] The application of the invention is not limited to theexemplified liquid crystal display devices. When one of a pair ofelectrodes for applying a voltage through a liquid crystal layer in apicture element region is formed to have a plurality of openingsdisposed at least at the corners of the picture element region and asolid portion, a liquid crystal display device with a wide viewing anglecharacteristic can be realized. When the electrode is formed in theaforementioned manner, inclined electric fields are generated at theedge portions of the openings of the electrode when a voltage isapplied. Accordingly, owing to the inclined electric fields generated atthe edge portions of the plural openings disposed at least at thecorners, liquid crystal domains that are in the radially-inclinedorientation state are formed in the liquid crystal layer under voltageapplication, resulting in obtaining a wide viewing angle characteristic.

[0269] A unit solid portion (a region of the solid portion substantiallysurrounded with the openings) present in a given picture element regionmay be plural in number or a single unit solid portion surrounded withthe openings disposed at the corners. In the case where the unit solidportion present in a given picture element region is single, theopenings surrounding the unit solid portion may be a plurality ofopenings disposed at the corners or a substantially single openingcontinuously formed from a plurality of openings disposed at thecorners.

[0270] When the region of the solid portion substantially surroundedwith the openings (unit solid portion) is rotationally symmetrical, thestability of the radially-inclined orientation of the liquid crystaldomain formed in the solid portion can be improved. For example, theunit solid portion may be in the shape of a substantially circle, asubstantially square or a substantially rectangle.

[0271] When the unit solid portion is in a substantially circular shape,the radially-inclined orientation of the liquid crystal domain formed inthe solid portion of the electrode can be stabilized. Since a liquidcrystal domain formed in the solid portion made from a continuousconducting film is formed correspondingly to the unit solid portion, theshape and the arrangement of the openings are determined so that theunit solid portion can be in the substantially circular shape. Also,when the unit solid portion is in a substantially rectangular shape withsubstantially arc-shaped corners, the orientation stability and thetransmittance (effective aperture ratio) can be comparatively increased.

[0272] According to the present invention, the liquid crystal domainshaving the radially-inclined orientation formed correspondingly to theopenings formed in the picture element electrode can also makecontribution to the display, and hence, the display quality of aconventional liquid crystal display device with a wide viewing anglecharacteristic can be further improved.

[0273] Moreover, when a protrusion is formed within the opening of thepicture element electrode, the stability of the radially-inclinedorientation is improved. Accordingly, it is possible to provide a liquidcrystal display device with high reliability in which even when theradially-inclined orientation is destroyed by an external force, theradially-inclined orientation can be easily restored.

1. A liquid crystal display device comprising: a first substrate; asecond substrate; a liquid crystal layer disposed between the firstsubstrate and the second substrate; and a plurality of picture elementregions each defined by a first electrode provided on a face of thefirst substrate facing the liquid crystal layer and a second electrodeprovided on the second substrate so as to oppose the first electrode viathe liquid crystal layer sandwiched therebetween, wherein the firstelectrode includes a plurality of openings and a solid portion in eachof the plurality of picture element regions, the liquid crystal layer isin a vertical orientation state in each of the plurality of pictureelement regions when no voltage is applied between the first electrodeand the second electrode, and when a voltage is applied between thefirst electrode and the second electrode, a plurality of liquid crystaldomains each in a radially-inclined orientation state are formed in theplurality of openings and the solid portion by inclined electric fieldsgenerated at respective edge portions of the plurality of openings ofthe first electrode, for producing a display by changing orientationstates of the plurality of liquid crystal domains in accordance with theapplied voltage.
 2. The liquid crystal display device of claim 1,wherein at least some of the plurality of openings have substantiallythe same shape and the same size, and form at least one unit latticearranged so as to have rotational symmetry.
 3. The liquid crystaldisplay device of claim 2, wherein each of the at least some of theplurality of openings is in a rotationally symmetrical shape.
 4. Theliquid crystal display device of claim 2, wherein each the of at leastsome of the plurality of openings is in a substantially circular shape.5. The liquid crystal display device of claim 2, wherein each region ofthe solid portion surrounded with the at least some of the plurality ofopenings is in a substantially circular shape.
 6. The liquid crystaldisplay device of claim 2, wherein each region of the solid portionsurrounded with the at least some of the plurality of openings is in asubstantially rectangular shape with substantially arc-shaped corners.7. The liquid crystal display device of claim 1, wherein, in each of theplurality of picture element regions, a total area of the plurality ofopenings of the first electrode is smaller than an area of the solidportion of the first electrode.
 8. The liquid crystal display device ofclaim 1, further comprising a protrusion within each of the plurality ofopenings, wherein a cross-sectional shape of the protrusion taken alonga plane direction of the substrate is the same as a shape of thecorresponding opening, and a side face of the protrusion has anorientation-regulating force for orienting liquid crystal molecules ofthe liquid crystal layer in the same direction as anorientation-regulating direction obtained by the inclined electricfield.
 9. The liquid crystal display device of claim 1, wherein theplurality of liquid crystal domains are in a spirally radially-inclinedorientation state.
 10. The liquid crystal display device of claim 9,further comprising a pair of polarizing plates respectively providedoutside of the first substrate and the second substrate and disposedwith polarizing axes thereof crossing each other substantiallyperpendicularly, wherein, in each of the plurality of liquid crystaldomains, assuming that a liquid crystal molecule included in the liquidcrystal layer and positioned in a 12 o'clock direction on a displaysurface in regard to a center of each of said plurality of liquidcrystal domains is inclined against the 12 o'clock direction on thedisplay surface by an angle θ, the polarization axis of one of the pairof polarizing plates is inclined in the same direction as inclination ofthe liquid crystal molecule positioned in the 12 o'clock direction onthe display surface by an angle exceeding 0 degree and smaller than 2θagainst the 12 o'clock direction on the display surface.
 11. The liquidcrystal display device of claim 10, wherein the polarization axis of oneof the pair of polarizing plates is inclined by an angle exceeding 0degree and equal to θ or less.
 12. The liquid crystal display device ofclaim 10, wherein the polarization axis of one of the pair of polarizingplates is inclined by an angle substantially the same as θ/2.
 13. Theliquid crystal display device of claim 10, wherein the polarization axisof one of the pair of polarizing plates is inclined by an anglesubstantially the same as θ.
 14. The liquid crystal display device ofclaim 1, wherein the solid portion includes a plurality of islandportions arranged in the form of an m×n matrix and a plurality of branchportions for electrically connecting adjacent pairs of the plurality ofisland portions, and the number of the plurality of branch portions issmaller than (2mn−m−n).
 15. The liquid crystal display device of claim1, wherein the first substrate further includes an active elementprovided correspondingly to each of the plurality of picture elementregions, and the first electrode corresponds to a picture elementelectrode provided in each of the plurality of picture element regionsto be switched by the active element and the second electrodecorresponds to at least one counter electrode opposing the plurality ofpicture element electrodes. 16-20. (Canceled)